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	$28.55	10.725%	$31.612	$31.61	$31.60	$31.60
Purchase #2	$167.69	11.386%	$186.7832	$186.78	$186.80	$186.80
Purchase #3	$58.51	10.306%	$64.54	$64.54	$64.55	$64.50
Purchase #4	$33.48	4.502%	$34.9873	$34.99	$35.00	$35.00
Purchase #5	$166.45	8.105%	$179.9408	$179.94	$179.95	$179.90
Purchase #6	$51.90	3.148%	$53.5338	$53.53	$53.55	$53.50
Purchase #7	$45.73	11.490%	$50.9844	$50.98	$51.00	$51.00
7 purchase totals =	$552.31		$602.3815	$602.37	$602.45	$602.30