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 $49.70   11.276%   $55.3042   $55.30   $55.30   $55.30  
  Purchase #2 $23.63   4.356%   $24.6593   $24.66   $24.65   $24.70  
  Purchase #3 $104.42   4.760%   $109.3904   $109.39   $109.40   $109.40  
  Purchase #4 $73.34   11.457%   $81.7426   $81.74   $81.75   $81.70  
  Purchase #5 $225.25   11.250%   $250.5906   $250.59   $250.60   $250.60  
  Purchase #6 $188.56   9.655%   $206.7655   $206.77   $206.75   $206.80  
  Purchase #7 $72.84   3.718%   $75.5482   $75.55   $75.55   $75.50  
  7 purchase totals = $737.74       $804.0008   $804.00   $804.00   $804.00