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 $116.53   9.594%   $127.7099   $127.71   $127.70   $127.70  
  Purchase #2 $93.95   11.147%   $104.4226   $104.42   $104.40   $104.40  
  Purchase #3 $124.35   6.253%   $132.1256   $132.13   $132.15   $132.10  
  Purchase #4 $134.94   9.507%   $147.7687   $147.77   $147.75   $147.80  
  Purchase #5 $49.76   8.859%   $54.1682   $54.17   $54.15   $54.20  
  Purchase #6 $32.43   11.544%   $36.1737   $36.17   $36.15   $36.20  
  Purchase #7 $168.83   6.843%   $180.383   $180.38   $180.40   $180.40  
  7 purchase totals = $720.79       $782.7517   $782.75   $782.70   $782.80