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 $52.71   13.129%   $59.6303   $59.63   $59.65   $59.60  
  Purchase #2 $164.57   12.678%   $185.4342   $185.43   $185.45   $185.40  
  Purchase #3 $50.74   6.261%   $53.9168   $53.92   $53.90   $53.90  
  Purchase #4 $125.63   10.373%   $138.6616   $138.66   $138.65   $138.70  
  Purchase #5 $211.54   11.108%   $235.0379   $235.04   $235.05   $235.00  
  Purchase #6 $180.99   6.647%   $193.0204   $193.02   $193.00   $193.00  
  Purchase #7 $103.98   13.165%   $117.669   $117.67   $117.65   $117.70  
  7 purchase totals = $890.16       $983.3702   $983.37   $983.35   $983.30