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 $231.62   10.789%   $256.6095   $256.61   $256.60   $256.60  
  Purchase #2 $207.37   6.395%   $220.6313   $220.63   $220.65   $220.60  
  Purchase #3 $97.50   10.558%   $107.7941   $107.79   $107.80   $107.80  
  Purchase #4 $83.43   13.645%   $94.814   $94.81   $94.80   $94.80  
  Purchase #5 $95.49   9.211%   $104.2856   $104.29   $104.30   $104.30  
  Purchase #6 $41.44   12.221%   $46.5044   $46.50   $46.50   $46.50  
  Purchase #7 $194.78   12.733%   $219.5813   $219.58   $219.60   $219.60  
  7 purchase totals = $951.63       $1,050.2202   $1,050.21   $1,050.25   $1,050.20