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 $188.75   8.454%   $204.7069   $204.71   $204.70   $204.70  
  Purchase #2 $145.53   9.441%   $159.2695   $159.27   $159.25   $159.30  
  Purchase #3 $32.98   9.370%   $36.0702   $36.07   $36.05   $36.10  
  Purchase #4 $175.78   8.165%   $190.1324   $190.13   $190.15   $190.10  
  Purchase #5 $90.45   4.464%   $94.4877   $94.49   $94.50   $94.50  
  Purchase #6 $32.40   6.441%   $34.4869   $34.49   $34.50   $34.50  
  Purchase #7 $36.63   11.200%   $40.7326   $40.73   $40.75   $40.70  
  7 purchase totals = $702.52       $759.8862   $759.89   $759.90   $759.90