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 $96.33   8.142%   $104.1732   $104.17   $104.15   $104.20  
  Purchase #2 $244.31   7.612%   $262.9069   $262.91   $262.90   $262.90  
  Purchase #3 $117.43   9.359%   $128.4203   $128.42   $128.40   $128.40  
  Purchase #4 $204.30   13.682%   $232.2523   $232.25   $232.25   $232.30  
  Purchase #5 $242.98   7.730%   $261.7624   $261.76   $261.75   $261.80  
  Purchase #6 $199.34   10.565%   $220.4003   $220.40   $220.40   $220.40  
  Purchase #7 $130.86   8.405%   $141.8588   $141.86   $141.85   $141.90  
  7 purchase totals = $1,235.55       $1,351.7742   $1,351.77   $1,351.70   $1,351.90