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 $88.55   10.114%   $97.5059   $97.51   $97.50   $97.50  
  Purchase #2 $68.38   5.271%   $71.9843   $71.98   $72.00   $72.00  
  Purchase #3 $34.25   5.801%   $36.2368   $36.24   $36.25   $36.20  
  Purchase #4 $161.71   5.684%   $170.9016   $170.90   $170.90   $170.90  
  Purchase #5 $116.28   12.274%   $130.5522   $130.55   $130.55   $130.60  
  Purchase #6 $224.29   7.597%   $241.3293   $241.33   $241.35   $241.30  
  Purchase #7 $236.87   4.589%   $247.74   $247.74   $247.75   $247.70  
  7 purchase totals = $930.33       $996.2501   $996.25   $996.30   $996.20