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 $225.35   7.219%   $241.618   $241.62   $241.60   $241.60  
  Purchase #2 $50.68   7.490%   $54.4759   $54.48   $54.50   $54.50  
  Purchase #3 $55.96   5.224%   $58.8834   $58.88   $58.90   $58.90  
  Purchase #4 $150.63   7.613%   $162.0975   $162.10   $162.10   $162.10  
  Purchase #5 $135.93   6.189%   $144.3427   $144.34   $144.35   $144.30  
  Purchase #6 $23.75   4.864%   $24.9052   $24.91   $24.90   $24.90  
  Purchase #7 $248.98   5.475%   $262.6117   $262.61   $262.60   $262.60  
  7 purchase totals = $891.28       $948.9344   $948.94   $948.95   $948.90