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 $207.83   9.624%   $227.8316   $227.83   $227.85   $227.80  
  Purchase #2 $91.73   11.605%   $102.3753   $102.38   $102.40   $102.40  
  Purchase #3 $64.68   13.218%   $73.2294   $73.23   $73.25   $73.20  
  Purchase #4 $57.83   10.616%   $63.9692   $63.97   $63.95   $64.00  
  Purchase #5 $244.82   6.717%   $261.2646   $261.26   $261.25   $261.30  
  Purchase #6 $211.83   13.160%   $239.7068   $239.71   $239.70   $239.70  
  Purchase #7 $45.42   6.744%   $48.4831   $48.48   $48.50   $48.50  
  7 purchase totals = $924.14       $1,016.8600   $1,016.86   $1,016.90   $1,016.90