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 $96.41   5.752%   $101.9555   $101.96   $101.95   $102.00  
  Purchase #2 $78.76   3.540%   $81.5481   $81.55   $81.55   $81.50  
  Purchase #3 $159.27   6.394%   $169.4537   $169.45   $169.45   $169.50  
  Purchase #4 $207.66   5.532%   $219.1478   $219.15   $219.15   $219.10  
  Purchase #5 $31.43   7.803%   $33.8825   $33.88   $33.90   $33.90  
  Purchase #6 $72.56   11.859%   $81.1649   $81.16   $81.15   $81.20  
  Purchase #7 $182.29   8.398%   $197.5987   $197.60   $197.60   $197.60  
  7 purchase totals = $828.38       $884.7512   $884.75   $884.75   $884.80