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	$143.71	11.595%	$160.3732	$160.37	$160.35	$160.40
Purchase #2	$233.51	4.308%	$243.5696	$243.57	$243.55	$243.60
Purchase #3	$174.88	5.696%	$184.8412	$184.84	$184.85	$184.80
Purchase #4	$163.62	10.795%	$181.2828	$181.28	$181.30	$181.30
Purchase #5	$233.76	8.840%	$254.4244	$254.42	$254.40	$254.40
Purchase #6	$52.79	3.325%	$54.5453	$54.55	$54.55	$54.50
Purchase #7	$24.59	7.654%	$26.4721	$26.47	$26.45	$26.50
7 purchase totals =	$1,026.86		$1,105.5086	$1,105.50	$1,105.45	$1,105.50