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 $57.53   5.520%   $60.7057   $60.71   $60.70   $60.70  
  Purchase #2 $157.47   5.631%   $166.3371   $166.34   $166.35   $166.30  
  Purchase #3 $207.64   5.801%   $219.6852   $219.69   $219.70   $219.70  
  Purchase #4 $73.41   11.506%   $81.8566   $81.86   $81.85   $81.90  
  Purchase #5 $21.52   13.409%   $24.4056   $24.41   $24.40   $24.40  
  Purchase #6 $12.64   12.636%   $14.2372   $14.24   $14.25   $14.20  
  Purchase #7 $188.76   5.439%   $199.0267   $199.03   $199.05   $199.00  
  7 purchase totals = $718.97       $766.2541   $766.28   $766.30   $766.20