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 $236.65   9.578%   $259.3163   $259.32   $259.30   $259.30  
  Purchase #2 $131.39   8.145%   $142.0917   $142.09   $142.10   $142.10  
  Purchase #3 $60.75   9.172%   $66.322   $66.32   $66.30   $66.30  
  Purchase #4 $225.71   5.154%   $237.3431   $237.34   $237.35   $237.30  
  Purchase #5 $12.84   12.730%   $14.4745   $14.47   $14.45   $14.50  
  Purchase #6 $229.71   8.206%   $248.56   $248.56   $248.55   $248.60  
  Purchase #7 $217.31   11.433%   $242.1551   $242.16   $242.15   $242.20  
  7 purchase totals = $1,114.36       $1,210.2627   $1,210.26   $1,210.20   $1,210.30