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 $192.35   6.794%   $205.4183   $205.42   $205.40   $205.40  
  Purchase #2 $248.59   6.374%   $264.4351   $264.44   $264.45   $264.40  
  Purchase #3 $242.86   7.738%   $261.6525   $261.65   $261.65   $261.70  
  Purchase #4 $208.92   4.234%   $217.7657   $217.77   $217.75   $217.80  
  Purchase #5 $87.99   8.410%   $95.39   $95.39   $95.40   $95.40  
  Purchase #6 $16.94   12.386%   $19.0382   $19.04   $19.05   $19.00  
  Purchase #7 $156.96   13.503%   $178.1543   $178.15   $178.15   $178.20  
  7 purchase totals = $1,154.61       $1,241.8541   $1,241.86   $1,241.85   $1,241.90