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	$117.91	8.419%	$127.8368	$127.84	$127.85	$127.80
Purchase #2	$59.59	5.104%	$62.6315	$62.63	$62.65	$62.60
Purchase #3	$162.93	10.187%	$179.5277	$179.53	$179.55	$179.50
Purchase #4	$117.80	13.561%	$133.7749	$133.77	$133.75	$133.80
Purchase #5	$34.60	3.721%	$35.8875	$35.89	$35.90	$35.90
Purchase #6	$177.73	4.644%	$185.9838	$185.98	$186.00	$186.00
Purchase #7	$50.57	13.748%	$57.5224	$57.52	$57.50	$57.50
7 purchase totals =	$721.13		$783.1646	$783.16	$783.20	$783.10