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 $244.28   7.600%   $262.8453   $262.85   $262.85   $262.80  
  Purchase #2 $109.35   9.616%   $119.8651   $119.87   $119.85   $119.90  
  Purchase #3 $29.99   7.159%   $32.137   $32.14   $32.15   $32.10  
  Purchase #4 $117.38   7.302%   $125.9511   $125.95   $125.95   $126.00  
  Purchase #5 $66.90   11.102%   $74.3272   $74.33   $74.35   $74.30  
  Purchase #6 $228.92   11.563%   $255.39   $255.39   $255.40   $255.40  
  Purchase #7 $195.49   10.416%   $215.8522   $215.85   $215.85   $215.90  
  7 purchase totals = $992.31       $1,086.3679   $1,086.38   $1,086.40   $1,086.40