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 $123.95   8.659%   $134.6828   $134.68   $134.70   $134.70  
  Purchase #2 $189.33   7.400%   $203.3404   $203.34   $203.35   $203.30  
  Purchase #3 $104.75   12.606%   $117.9548   $117.95   $117.95   $118.00  
  Purchase #4 $116.25   13.858%   $132.3599   $132.36   $132.35   $132.40  
  Purchase #5 $192.38   11.494%   $214.4922   $214.49   $214.50   $214.50  
  Purchase #6 $207.74   12.593%   $233.9007   $233.90   $233.90   $233.90  
  Purchase #7 $174.74   12.123%   $195.9237   $195.92   $195.90   $195.90  
  7 purchase totals = $1,109.14       $1,232.6545   $1,232.64   $1,232.65   $1,232.70