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 $197.61   7.807%   $213.0374   $213.04   $213.05   $213.00  
  Purchase #2 $173.73   9.463%   $190.1701   $190.17   $190.15   $190.20  
  Purchase #3 $46.48   11.606%   $51.8745   $51.87   $51.85   $51.90  
  Purchase #4 $126.47   7.703%   $136.212   $136.21   $136.20   $136.20  
  Purchase #5 $136.46   13.541%   $154.938   $154.94   $154.95   $154.90  
  Purchase #6 $223.69   13.864%   $254.7024   $254.70   $254.70   $254.70  
  Purchase #7 $231.51   4.160%   $241.1408   $241.14   $241.15   $241.10  
  7 purchase totals = $1,135.95       $1,242.0752   $1,242.07   $1,242.05   $1,242.00