Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $60.91   9.780%   $66.867   $66.87   $66.85   $66.90  
  Purchase #2 $196.43   11.456%   $218.933   $218.93   $218.95   $218.90  
  Purchase #3 $139.34   9.797%   $152.9911   $152.99   $153.00   $153.00  
  Purchase #4 $45.81   7.741%   $49.3562   $49.36   $49.35   $49.40  
  Purchase #5 $245.96   13.707%   $279.6737   $279.67   $279.65   $279.70  
  Purchase #6 $109.28   9.688%   $119.867   $119.87   $119.85   $119.90  
  Purchase #7 $174.97   3.488%   $181.073   $181.07   $181.05   $181.10  
  7 purchase totals = $972.70       $1,068.7610   $1,068.76   $1,068.70   $1,068.90