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 $148.83   9.272%   $162.6295   $162.63   $162.65   $162.60  
  Purchase #2 $67.39   13.865%   $76.7336   $76.73   $76.75   $76.70  
  Purchase #3 $87.93   6.843%   $93.947   $93.95   $93.95   $93.90  
  Purchase #4 $115.58   9.108%   $126.107   $126.11   $126.10   $126.10  
  Purchase #5 $24.45   10.194%   $26.9424   $26.94   $26.95   $26.90  
  Purchase #6 $219.79   12.749%   $247.811   $247.81   $247.80   $247.80  
  Purchase #7 $209.26   12.823%   $236.0934   $236.09   $236.10   $236.10  
  7 purchase totals = $873.23       $970.2639   $970.26   $970.30   $970.10