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 $63.31   11.398%   $70.5261   $70.53   $70.55   $70.50  
  Purchase #2 $96.28   8.160%   $104.1364   $104.14   $104.15   $104.10  
  Purchase #3 $108.67   3.485%   $112.4571   $112.46   $112.45   $112.50  
  Purchase #4 $190.65   8.825%   $207.4749   $207.47   $207.45   $207.50  
  Purchase #5 $76.86   8.183%   $83.1495   $83.15   $83.15   $83.10  
  Purchase #6 $192.87   4.652%   $201.8423   $201.84   $201.85   $201.80  
  Purchase #7 $163.95   7.702%   $176.5774   $176.58   $176.60   $176.60  
  7 purchase totals = $892.59       $956.1637   $956.17   $956.20   $956.10