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 $38.83   13.401%   $44.0336   $44.03   $44.05   $44.00  
  Purchase #2 $148.54   3.476%   $153.7033   $153.70   $153.70   $153.70  
  Purchase #3 $99.68   3.102%   $102.7721   $102.77   $102.75   $102.80  
  Purchase #4 $131.49   11.465%   $146.5653   $146.57   $146.55   $146.60  
  Purchase #5 $209.30   3.386%   $216.3869   $216.39   $216.40   $216.40  
  Purchase #6 $167.36   8.765%   $182.0291   $182.03   $182.05   $182.00  
  Purchase #7 $190.27   3.833%   $197.563   $197.56   $197.55   $197.60  
  7 purchase totals = $985.47       $1,043.0533   $1,043.05   $1,043.05   $1,043.10