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 $201.86   12.416%   $226.9229   $226.92   $226.90   $226.90  
  Purchase #2 $155.97   10.874%   $172.9302   $172.93   $172.95   $172.90  
  Purchase #3 $249.83   5.842%   $264.4251   $264.43   $264.45   $264.40  
  Purchase #4 $76.61   12.650%   $86.3012   $86.30   $86.30   $86.30  
  Purchase #5 $86.75   7.116%   $92.9231   $92.92   $92.90   $92.90  
  Purchase #6 $231.60   11.175%   $257.4813   $257.48   $257.50   $257.50  
  Purchase #7 $163.63   3.257%   $168.9594   $168.96   $168.95   $169.00  
  7 purchase totals = $1,166.25       $1,269.9432   $1,269.94   $1,269.95   $1,269.90