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	$230.47	8.637%	$250.3757	$250.38	$250.40	$250.40
Purchase #2	$60.80	11.365%	$67.7099	$67.71	$67.70	$67.70
Purchase #3	$94.50	5.354%	$99.5595	$99.56	$99.55	$99.60
Purchase #4	$124.66	4.823%	$130.6724	$130.67	$130.65	$130.70
Purchase #5	$234.82	9.167%	$256.3459	$256.35	$256.35	$256.30
Purchase #6	$162.84	6.616%	$173.6135	$173.61	$173.60	$173.60
Purchase #7	$158.66	8.761%	$172.5602	$172.56	$172.55	$172.60
7 purchase totals =	$1,066.75		$1,150.8371	$1,150.84	$1,150.80	$1,150.90