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 $94.69   8.177%   $102.4328   $102.43   $102.45   $102.40  
  Purchase #2 $97.49   9.399%   $106.6531   $106.65   $106.65   $106.70  
  Purchase #3 $68.30   11.237%   $75.9749   $75.97   $75.95   $76.00  
  Purchase #4 $202.44   11.781%   $226.2895   $226.29   $226.30   $226.30  
  Purchase #5 $228.53   10.775%   $253.1541   $253.15   $253.15   $253.20  
  Purchase #6 $50.78   9.834%   $55.7737   $55.77   $55.75   $55.80  
  Purchase #7 $76.37   8.634%   $82.9638   $82.96   $82.95   $83.00  
  7 purchase totals = $818.60       $903.2419   $903.22   $903.20   $903.40