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	$118.75	12.146%	$133.1734	$133.17	$133.15	$133.20
Purchase #2	$22.57	6.600%	$24.0596	$24.06	$24.05	$24.10
Purchase #3	$93.95	5.725%	$99.3286	$99.33	$99.35	$99.30
Purchase #4	$40.57	3.731%	$42.0837	$42.08	$42.10	$42.10
Purchase #5	$61.38	6.656%	$65.4655	$65.47	$65.45	$65.50
Purchase #6	$50.62	6.810%	$54.0672	$54.07	$54.05	$54.10
Purchase #7	$36.65	10.292%	$40.422	$40.42	$40.40	$40.40
7 purchase totals =	$424.49		$458.6000	$458.60	$458.55	$458.70