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 $196.65   7.309%   $211.0231   $211.02   $211.00   $211.00  
  Purchase #2 $85.67   3.241%   $88.4466   $88.45   $88.45   $88.40  
  Purchase #3 $194.89   5.804%   $206.2014   $206.20   $206.20   $206.20  
  Purchase #4 $140.56   10.768%   $155.6955   $155.70   $155.70   $155.70  
  Purchase #5 $93.63   8.491%   $101.5801   $101.58   $101.60   $101.60  
  Purchase #6 $170.93   5.846%   $180.9226   $180.92   $180.90   $180.90  
  Purchase #7 $73.38   5.311%   $77.2772   $77.28   $77.30   $77.30  
  7 purchase totals = $955.71       $1,021.1465   $1,021.15   $1,021.15   $1,021.10