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 $167.43   4.873%   $175.5889   $175.59   $175.60   $175.60  
  Purchase #2 $62.75   3.468%   $64.9262   $64.93   $64.95   $64.90  
  Purchase #3 $146.81   4.289%   $153.1067   $153.11   $153.10   $153.10  
  Purchase #4 $168.36   11.323%   $187.4234   $187.42   $187.40   $187.40  
  Purchase #5 $36.86   13.579%   $41.8652   $41.87   $41.85   $41.90  
  Purchase #6 $53.65   4.733%   $56.1893   $56.19   $56.20   $56.20  
  Purchase #7 $151.26   13.655%   $171.9146   $171.91   $171.90   $171.90  
  7 purchase totals = $787.12       $851.0143   $851.02   $851.00   $851.00