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 $104.66   13.855%   $119.1606   $119.16   $119.15   $119.20  
  Purchase #2 $188.82   8.741%   $205.3248   $205.32   $205.30   $205.30  
  Purchase #3 $21.98   4.502%   $22.9695   $22.97   $22.95   $23.00  
  Purchase #4 $245.72   10.515%   $271.5575   $271.56   $271.55   $271.60  
  Purchase #5 $94.26   9.793%   $103.4909   $103.49   $103.50   $103.50  
  Purchase #6 $85.43   3.219%   $88.18   $88.18   $88.20   $88.20  
  Purchase #7 $110.74   3.379%   $114.4819   $114.48   $114.50   $114.50  
  7 purchase totals = $851.61       $925.1652   $925.16   $925.15   $925.30