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	$57.54	4.817%	$60.3117	$60.31	$60.30	$60.30
Purchase #2	$48.74	7.530%	$52.4101	$52.41	$52.40	$52.40
Purchase #3	$174.52	5.745%	$184.5462	$184.55	$184.55	$184.50
Purchase #4	$37.36	8.730%	$40.6215	$40.62	$40.60	$40.60
Purchase #5	$138.42	3.243%	$142.909	$142.91	$142.90	$142.90
Purchase #6	$20.73	6.818%	$22.1434	$22.14	$22.15	$22.10
Purchase #7	$47.35	12.785%	$53.4037	$53.40	$53.40	$53.40
7 purchase totals =	$524.66		$556.3456	$556.34	$556.30	$556.20