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 $62.85   5.301%   $66.1817   $66.18   $66.20   $66.20  
  Purchase #2 $194.30   3.602%   $201.2987   $201.30   $201.30   $201.30  
  Purchase #3 $209.43   9.778%   $229.9081   $229.91   $229.90   $229.90  
  Purchase #4 $121.59   12.747%   $137.0891   $137.09   $137.10   $137.10  
  Purchase #5 $66.63   9.801%   $73.1604   $73.16   $73.15   $73.20  
  Purchase #6 $61.42   8.646%   $66.7304   $66.73   $66.75   $66.70  
  Purchase #7 $46.96   13.425%   $53.2644   $53.26   $53.25   $53.30  
  7 purchase totals = $763.18       $827.6328   $827.63   $827.65   $827.70