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 $42.76   4.213%   $44.5615   $44.56   $44.55   $44.60  
  Purchase #2 $226.72   10.583%   $250.7138   $250.71   $250.70   $250.70  
  Purchase #3 $250.60   6.172%   $266.067   $266.07   $266.05   $266.10  
  Purchase #4 $14.59   12.634%   $16.4333   $16.43   $16.45   $16.40  
  Purchase #5 $105.29   6.749%   $112.396   $112.40   $112.40   $112.40  
  Purchase #6 $210.97   12.507%   $237.356   $237.36   $237.35   $237.40  
  Purchase #7 $66.91   13.287%   $75.8003   $75.80   $75.80   $75.80  
  7 purchase totals = $917.84       $1,003.3279   $1,003.33   $1,003.30   $1,003.40