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 $125.72   7.394%   $135.0157   $135.02   $135.00   $135.00  
  Purchase #2 $116.95   5.360%   $123.2185   $123.22   $123.20   $123.20  
  Purchase #3 $217.81   5.218%   $229.1753   $229.18   $229.20   $229.20  
  Purchase #4 $43.97   6.754%   $46.9397   $46.94   $46.95   $46.90  
  Purchase #5 $147.30   7.295%   $158.0455   $158.05   $158.05   $158.00  
  Purchase #6 $113.74   6.123%   $120.7043   $120.70   $120.70   $120.70  
  Purchase #7 $170.44   7.359%   $182.9827   $182.98   $183.00   $183.00  
  7 purchase totals = $935.93       $996.0817   $996.09   $996.10   $996.00