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 $232.73   8.397%   $252.2723   $252.27   $252.25   $252.30  
  Purchase #2 $220.42   12.316%   $247.5669   $247.57   $247.55   $247.60  
  Purchase #3 $83.78   6.562%   $89.2776   $89.28   $89.30   $89.30  
  Purchase #4 $107.98   4.457%   $112.7927   $112.79   $112.80   $112.80  
  Purchase #5 $180.49   3.612%   $187.0093   $187.01   $187.00   $187.00  
  Purchase #6 $208.48   8.257%   $225.6942   $225.69   $225.70   $225.70  
  Purchase #7 $127.77   10.191%   $140.791   $140.79   $140.80   $140.80  
  7 purchase totals = $1,161.65       $1,255.4040   $1,255.40   $1,255.40   $1,255.50