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 $236.63   10.684%   $261.9115   $261.91   $261.90   $261.90  
  Purchase #2 $154.93   12.861%   $174.8555   $174.86   $174.85   $174.90  
  Purchase #3 $176.27   12.117%   $197.6286   $197.63   $197.65   $197.60  
  Purchase #4 $55.86   10.499%   $61.7247   $61.72   $61.70   $61.70  
  Purchase #5 $141.80   10.445%   $156.611   $156.61   $156.60   $156.60  
  Purchase #6 $146.30   9.689%   $160.475   $160.48   $160.50   $160.50  
  Purchase #7 $185.34   10.546%   $204.886   $204.89   $204.90   $204.90  
  7 purchase totals = $1,097.13       $1,218.0923   $1,218.10   $1,218.10   $1,218.10