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 $88.78   9.534%   $97.2443   $97.24   $97.25   $97.20  
  Purchase #2 $46.56   11.110%   $51.7328   $51.73   $51.75   $51.70  
  Purchase #3 $103.71   13.688%   $117.9058   $117.91   $117.90   $117.90  
  Purchase #4 $30.55   10.409%   $33.7299   $33.73   $33.75   $33.70  
  Purchase #5 $219.72   12.153%   $246.4226   $246.42   $246.40   $246.40  
  Purchase #6 $211.46   5.706%   $223.5259   $223.53   $223.55   $223.50  
  Purchase #7 $146.65   6.644%   $156.3934   $156.39   $156.40   $156.40  
  7 purchase totals = $847.43       $926.9547   $926.95   $927.00   $926.80