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 $151.87   10.428%   $167.707   $167.71   $167.70   $167.70  
  Purchase #2 $240.77   4.215%   $250.9185   $250.92   $250.90   $250.90  
  Purchase #3 $92.42   6.474%   $98.4033   $98.40   $98.40   $98.40  
  Purchase #4 $242.35   8.806%   $263.6913   $263.69   $263.70   $263.70  
  Purchase #5 $225.25   11.431%   $250.9983   $251.00   $251.00   $251.00  
  Purchase #6 $94.64   10.773%   $104.8356   $104.84   $104.85   $104.80  
  Purchase #7 $56.73   13.299%   $64.2745   $64.27   $64.25   $64.30  
  7 purchase totals = $1,104.03       $1,200.8285   $1,200.83   $1,200.80   $1,200.80