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 $231.73   13.846%   $263.8153   $263.82   $263.80   $263.80  
  Purchase #2 $198.92   3.681%   $206.2422   $206.24   $206.25   $206.20  
  Purchase #3 $54.80   11.805%   $61.2691   $61.27   $61.25   $61.30  
  Purchase #4 $210.62   12.527%   $237.0044   $237.00   $237.00   $237.00  
  Purchase #5 $156.87   8.229%   $169.7788   $169.78   $169.80   $169.80  
  Purchase #6 $10.39   10.563%   $11.4875   $11.49   $11.50   $11.50  
  Purchase #7 $32.28   9.607%   $35.3811   $35.38   $35.40   $35.40  
  7 purchase totals = $895.61       $984.9784   $984.98   $985.00   $985.00