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 $176.31   10.721%   $195.2122   $195.21   $195.20   $195.20  
  Purchase #2 $248.81   12.111%   $278.9434   $278.94   $278.95   $278.90  
  Purchase #3 $210.94   13.217%   $238.8199   $238.82   $238.80   $238.80  
  Purchase #4 $33.95   11.134%   $37.73   $37.73   $37.75   $37.70  
  Purchase #5 $9.27   4.662%   $9.7022   $9.70   $9.70   $9.70  
  Purchase #6 $153.87   10.388%   $169.854   $169.85   $169.85   $169.90  
  Purchase #7 $133.47   4.682%   $139.7191   $139.72   $139.70   $139.70  
  7 purchase totals = $966.62       $1,069.9808   $1,069.97   $1,069.95   $1,069.90