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 $84.50   12.110%   $94.733   $94.73   $94.75   $94.70  
  Purchase #2 $194.95   3.757%   $202.2743   $202.27   $202.25   $202.30  
  Purchase #3 $219.73   3.197%   $226.7548   $226.75   $226.75   $226.80  
  Purchase #4 $93.48   11.653%   $104.3732   $104.37   $104.35   $104.40  
  Purchase #5 $174.28   6.665%   $185.8958   $185.90   $185.90   $185.90  
  Purchase #6 $51.42   5.511%   $54.2538   $54.25   $54.25   $54.30  
  Purchase #7 $84.83   7.302%   $91.0243   $91.02   $91.00   $91.00  
  7 purchase totals = $903.19       $959.3092   $959.29   $959.25   $959.40