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 $68.63   10.181%   $75.6172   $75.62   $75.60   $75.60  
  Purchase #2 $232.75   6.108%   $246.9664   $246.97   $246.95   $247.00  
  Purchase #3 $17.36   12.418%   $19.5158   $19.52   $19.50   $19.50  
  Purchase #4 $31.87   8.387%   $34.5429   $34.54   $34.55   $34.50  
  Purchase #5 $48.46   5.303%   $51.0298   $51.03   $51.05   $51.00  
  Purchase #6 $57.88   7.381%   $62.1521   $62.15   $62.15   $62.20  
  Purchase #7 $92.51   13.273%   $104.7889   $104.79   $104.80   $104.80  
  7 purchase totals = $549.46       $594.6131   $594.62   $594.60   $594.60