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 $244.28   7.170%   $261.7949   $261.79   $261.80   $261.80  
  Purchase #2 $89.78   6.271%   $95.4101   $95.41   $95.40   $95.40  
  Purchase #3 $59.39   8.735%   $64.5777   $64.58   $64.60   $64.60  
  Purchase #4 $136.63   7.545%   $146.9387   $146.94   $146.95   $146.90  
  Purchase #5 $166.58   3.644%   $172.6502   $172.65   $172.65   $172.70  
  Purchase #6 $38.90   13.474%   $44.1414   $44.14   $44.15   $44.10  
  Purchase #7 $166.88   8.580%   $181.1983   $181.20   $181.20   $181.20  
  7 purchase totals = $902.44       $966.7113   $966.71   $966.75   $966.70