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 $127.52   7.460%   $137.033   $137.03   $137.05   $137.00  
  Purchase #2 $50.59   5.848%   $53.5485   $53.55   $53.55   $53.50  
  Purchase #3 $122.81   5.608%   $129.6972   $129.70   $129.70   $129.70  
  Purchase #4 $103.29   8.633%   $112.207   $112.21   $112.20   $112.20  
  Purchase #5 $202.56   5.506%   $213.713   $213.71   $213.70   $213.70  
  Purchase #6 $64.53   3.595%   $66.8499   $66.85   $66.85   $66.80  
  Purchase #7 $198.69   9.357%   $217.2814   $217.28   $217.30   $217.30  
  7 purchase totals = $869.99       $930.3300   $930.33   $930.35   $930.20