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 $117.94   6.582%   $125.7028   $125.70   $125.70   $125.70  
  Purchase #2 $92.97   12.696%   $104.7735   $104.77   $104.75   $104.80  
  Purchase #3 $178.49   4.175%   $185.942   $185.94   $185.95   $185.90  
  Purchase #4 $117.29   10.560%   $129.6758   $129.68   $129.70   $129.70  
  Purchase #5 $6.26   7.831%   $6.7502   $6.75   $6.75   $6.80  
  Purchase #6 $5.71   5.430%   $6.0201   $6.02   $6.00   $6.00  
  Purchase #7 $112.35   3.637%   $116.4362   $116.44   $116.45   $116.40  
  7 purchase totals = $631.01       $675.3006   $675.30   $675.30   $675.30