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 $205.50   7.822%   $221.5742   $221.57   $221.55   $221.60  
  Purchase #2 $246.76   4.291%   $257.3485   $257.35   $257.35   $257.30  
  Purchase #3 $78.27   12.660%   $88.179   $88.18   $88.20   $88.20  
  Purchase #4 $203.88   4.534%   $213.1239   $213.12   $213.10   $213.10  
  Purchase #5 $194.51   6.796%   $207.7289   $207.73   $207.75   $207.70  
  Purchase #6 $57.42   5.186%   $60.3978   $60.40   $60.40   $60.40  
  Purchase #7 $175.48   9.803%   $192.6823   $192.68   $192.70   $192.70  
  7 purchase totals = $1,161.82       $1,241.0346   $1,241.03   $1,241.05   $1,241.00