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	$242.77	8.777%	$264.0779	$264.08	$264.10	$264.10
Purchase #2	$220.40	9.647%	$241.662	$241.66	$241.65	$241.70
Purchase #3	$207.59	5.329%	$218.6525	$218.65	$218.65	$218.70
Purchase #4	$39.29	11.166%	$43.6771	$43.68	$43.70	$43.70
Purchase #5	$88.34	12.249%	$99.1608	$99.16	$99.15	$99.20
Purchase #6	$230.72	10.824%	$255.6931	$255.69	$255.70	$255.70
Purchase #7	$41.57	9.485%	$45.5129	$45.51	$45.50	$45.50
7 purchase totals =	$1,070.68		$1,168.4363	$1,168.43	$1,168.45	$1,168.60