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 $137.92   9.526%   $151.0583   $151.06   $151.05   $151.10  
  Purchase #2 $114.92   13.296%   $130.1998   $130.20   $130.20   $130.20  
  Purchase #3 $20.31   8.597%   $22.0561   $22.06   $22.05   $22.10  
  Purchase #4 $14.27   9.290%   $15.5957   $15.60   $15.60   $15.60  
  Purchase #5 $42.97   8.811%   $46.7561   $46.76   $46.75   $46.80  
  Purchase #6 $227.37   11.799%   $254.1974   $254.20   $254.20   $254.20  
  Purchase #7 $64.30   4.863%   $67.4269   $67.43   $67.45   $67.40  
  7 purchase totals = $622.06       $687.2903   $687.31   $687.30   $687.40