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	$172.55	4.497%	$180.3096	$180.31	$180.30	$180.30
Purchase #2	$126.90	10.413%	$140.1141	$140.11	$140.10	$140.10
Purchase #3	$50.39	3.301%	$52.0534	$52.05	$52.05	$52.10
Purchase #4	$115.71	7.827%	$124.7666	$124.77	$124.75	$124.80
Purchase #5	$74.40	10.397%	$82.1354	$82.14	$82.15	$82.10
Purchase #6	$246.61	7.255%	$264.5016	$264.50	$264.50	$264.50
Purchase #7	$63.72	12.378%	$71.6073	$71.61	$71.60	$71.60
7 purchase totals =	$850.28		$915.4880	$915.49	$915.45	$915.50