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 $244.68   7.543%   $263.1362   $263.14   $263.15   $263.10  
  Purchase #2 $81.81   11.698%   $91.3801   $91.38   $91.40   $91.40  
  Purchase #3 $107.84   7.733%   $116.1793   $116.18   $116.20   $116.20  
  Purchase #4 $68.53   12.253%   $76.927   $76.93   $76.95   $76.90  
  Purchase #5 $199.49   8.599%   $216.6441   $216.64   $216.65   $216.60  
  Purchase #6 $67.45   13.224%   $76.3696   $76.37   $76.35   $76.40  
  Purchase #7 $95.56   12.614%   $107.6139   $107.61   $107.60   $107.60  
  7 purchase totals = $865.36       $948.2502   $948.25   $948.30   $948.20