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	$212.76	8.291%	$230.3999	$230.40	$230.40	$230.40
Purchase #2	$227.89	5.432%	$240.269	$240.27	$240.25	$240.30
Purchase #3	$221.49	3.128%	$228.4182	$228.42	$228.40	$228.40
Purchase #4	$223.64	12.191%	$250.904	$250.90	$250.90	$250.90
Purchase #5	$53.78	3.644%	$55.7397	$55.74	$55.75	$55.70
Purchase #6	$136.49	5.233%	$143.6325	$143.63	$143.65	$143.60
Purchase #7	$35.77	12.378%	$40.1976	$40.20	$40.20	$40.20
7 purchase totals =	$1,111.82		$1,189.5609	$1,189.56	$1,189.55	$1,189.50