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 $238.29   3.800%   $247.345   $247.35   $247.35   $247.30  
  Purchase #2 $89.68   10.164%   $98.7951   $98.80   $98.80   $98.80  
  Purchase #3 $52.35   11.578%   $58.4111   $58.41   $58.40   $58.40  
  Purchase #4 $22.64   9.772%   $24.8524   $24.85   $24.85   $24.90  
  Purchase #5 $113.86   7.479%   $122.3756   $122.38   $122.40   $122.40  
  Purchase #6 $240.51   10.427%   $265.588   $265.59   $265.60   $265.60  
  Purchase #7 $164.91   6.210%   $175.1509   $175.15   $175.15   $175.20  
  7 purchase totals = $922.24       $992.5181   $992.53   $992.55   $992.60