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 $116.92   8.473%   $126.8266   $126.83   $126.85   $126.80  
  Purchase #2 $119.33   10.496%   $131.8549   $131.85   $131.85   $131.90  
  Purchase #3 $44.66   3.752%   $46.3356   $46.34   $46.35   $46.30  
  Purchase #4 $137.91   10.747%   $152.7312   $152.73   $152.75   $152.70  
  Purchase #5 $132.41   12.554%   $149.0328   $149.03   $149.05   $149.00  
  Purchase #6 $174.28   6.390%   $185.4165   $185.42   $185.40   $185.40  
  Purchase #7 $29.84   9.819%   $32.77   $32.77   $32.75   $32.80  
  7 purchase totals = $755.35       $824.9676   $824.97   $825.00   $824.90