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 $236.54   12.568%   $266.2683   $266.27   $266.25   $266.30  
  Purchase #2 $150.87   5.755%   $159.5526   $159.55   $159.55   $159.60  
  Purchase #3 $246.90   3.104%   $254.5638   $254.56   $254.55   $254.60  
  Purchase #4 $91.46   6.140%   $97.0756   $97.08   $97.10   $97.10  
  Purchase #5 $23.78   4.324%   $24.8082   $24.81   $24.80   $24.80  
  Purchase #6 $111.82   12.668%   $125.9854   $125.99   $126.00   $126.00  
  Purchase #7 $6.94   6.863%   $7.4163   $7.42   $7.40   $7.40  
  7 purchase totals = $868.31       $935.6702   $935.68   $935.65   $935.80