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	$223.82	12.871%	$252.6279	$252.63	$252.65	$252.60
Purchase #2	$40.44	12.699%	$45.5755	$45.58	$45.60	$45.60
Purchase #3	$27.87	11.638%	$31.1135	$31.11	$31.10	$31.10
Purchase #4	$89.76	10.562%	$99.2405	$99.24	$99.25	$99.20
Purchase #5	$101.31	5.495%	$106.877	$106.88	$106.90	$106.90
Purchase #6	$74.38	5.491%	$78.4642	$78.46	$78.45	$78.50
Purchase #7	$240.56	5.492%	$253.7716	$253.77	$253.75	$253.80
7 purchase totals =	$798.14		$867.6702	$867.67	$867.70	$867.70