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	$171.51	12.499%	$192.947	$192.95	$192.95	$192.90
Purchase #2	$38.70	9.239%	$42.2755	$42.28	$42.30	$42.30
Purchase #3	$53.52	3.751%	$55.5275	$55.53	$55.55	$55.50
Purchase #4	$133.66	11.873%	$149.5295	$149.53	$149.55	$149.50
Purchase #5	$42.70	13.535%	$48.4794	$48.48	$48.50	$48.50
Purchase #6	$153.86	10.589%	$170.1522	$170.15	$170.15	$170.20
Purchase #7	$7.78	11.538%	$8.6777	$8.68	$8.70	$8.70
7 purchase totals =	$601.73		$667.5888	$667.60	$667.70	$667.60