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 $237.63   11.165%   $264.1614   $264.16   $264.15   $264.20  
  Purchase #2 $250.91   9.870%   $275.6748   $275.67   $275.65   $275.70  
  Purchase #3 $160.82   11.513%   $179.3352   $179.34   $179.35   $179.30  
  Purchase #4 $173.66   13.136%   $196.472   $196.47   $196.45   $196.50  
  Purchase #5 $248.82   9.445%   $272.321   $272.32   $272.30   $272.30  
  Purchase #6 $168.53   7.348%   $180.9136   $180.91   $180.90   $180.90  
  Purchase #7 $155.43   5.138%   $163.416   $163.42   $163.40   $163.40  
  7 purchase totals = $1,395.80       $1,532.2940   $1,532.29   $1,532.20   $1,532.30