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	$62.83	4.702%	$65.7843	$65.78	$65.80	$65.80
Purchase #2	$172.53	12.159%	$193.5079	$193.51	$193.50	$193.50
Purchase #3	$24.74	12.265%	$27.7744	$27.77	$27.75	$27.80
Purchase #4	$90.54	4.104%	$94.2558	$94.26	$94.25	$94.30
Purchase #5	$102.31	8.736%	$111.2478	$111.25	$111.25	$111.20
Purchase #6	$64.80	9.678%	$71.0713	$71.07	$71.05	$71.10
Purchase #7	$32.95	5.230%	$34.6733	$34.67	$34.65	$34.70
7 purchase totals =	$550.70		$598.3148	$598.31	$598.25	$598.40