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 $87.51   6.615%   $93.2988   $93.30   $93.30   $93.30  
  Purchase #2 $92.33   5.194%   $97.1256   $97.13   $97.15   $97.10  
  Purchase #3 $104.43   5.582%   $110.2593   $110.26   $110.25   $110.30  
  Purchase #4 $168.37   11.277%   $187.3571   $187.36   $187.35   $187.40  
  Purchase #5 $245.31   3.569%   $254.0651   $254.07   $254.05   $254.10  
  Purchase #6 $37.45   13.463%   $42.4919   $42.49   $42.50   $42.50  
  Purchase #7 $118.77   7.569%   $127.7597   $127.76   $127.75   $127.80  
  7 purchase totals = $854.17       $912.3575   $912.37   $912.35   $912.50