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 $76.62   11.139%   $85.1547   $85.15   $85.15   $85.20  
  Purchase #2 $143.38   4.339%   $149.6013   $149.60   $149.60   $149.60  
  Purchase #3 $224.88   11.162%   $249.9811   $249.98   $250.00   $250.00  
  Purchase #4 $210.32   3.550%   $217.7864   $217.79   $217.80   $217.80  
  Purchase #5 $65.33   3.382%   $67.5395   $67.54   $67.55   $67.50  
  Purchase #6 $174.42   8.285%   $188.8707   $188.87   $188.85   $188.90  
  Purchase #7 $59.54   12.209%   $66.8092   $66.81   $66.80   $66.80  
  7 purchase totals = $954.49       $1,025.7429   $1,025.74   $1,025.75   $1,025.80