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 $204.77   11.722%   $228.7731   $228.77   $228.75   $228.80  
  Purchase #2 $92.34   10.859%   $102.3672   $102.37   $102.35   $102.40  
  Purchase #3 $109.59   3.146%   $113.0377   $113.04   $113.05   $113.00  
  Purchase #4 $233.65   8.482%   $253.4682   $253.47   $253.45   $253.50  
  Purchase #5 $238.96   3.711%   $247.8278   $247.83   $247.85   $247.80  
  Purchase #6 $154.65   4.873%   $162.1861   $162.19   $162.20   $162.20  
  Purchase #7 $103.68   12.164%   $116.2916   $116.29   $116.30   $116.30  
  7 purchase totals = $1,137.64       $1,223.9517   $1,223.96   $1,223.95   $1,224.00