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 $47.63   6.594%   $50.7707   $50.77   $50.75   $50.80  
  Purchase #2 $44.39   8.433%   $48.1334   $48.13   $48.15   $48.10  
  Purchase #3 $70.37   6.645%   $75.0461   $75.05   $75.05   $75.00  
  Purchase #4 $91.94   3.426%   $95.0899   $95.09   $95.10   $95.10  
  Purchase #5 $172.29   7.733%   $185.6132   $185.61   $185.60   $185.60  
  Purchase #6 $175.34   5.114%   $184.3069   $184.31   $184.30   $184.30  
  Purchase #7 $238.37   7.397%   $256.0022   $256.00   $256.00   $256.00  
  7 purchase totals = $840.33       $894.9624   $894.96   $894.95   $894.90