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 $216.69   9.200%   $236.6255   $236.63   $236.65   $236.60  
  Purchase #2 $21.46   8.599%   $23.3053   $23.31   $23.30   $23.30  
  Purchase #3 $82.94   11.492%   $92.4715   $92.47   $92.45   $92.50  
  Purchase #4 $237.52   13.795%   $270.2859   $270.29   $270.30   $270.30  
  Purchase #5 $17.26   11.773%   $19.292   $19.29   $19.30   $19.30  
  Purchase #6 $61.55   9.253%   $67.2452   $67.25   $67.25   $67.20  
  Purchase #7 $102.70   7.498%   $110.4004   $110.40   $110.40   $110.40  
  7 purchase totals = $740.12       $819.6258   $819.64   $819.65   $819.60