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	$41.39	3.182%	$42.707	$42.71	$42.70	$42.70
Purchase #2	$116.51	9.631%	$127.7311	$127.73	$127.75	$127.70
Purchase #3	$115.52	4.202%	$120.3742	$120.37	$120.35	$120.40
Purchase #4	$85.40	5.434%	$90.0406	$90.04	$90.05	$90.00
Purchase #5	$57.78	6.738%	$61.6732	$61.67	$61.65	$61.70
Purchase #6	$27.89	10.752%	$30.8887	$30.89	$30.90	$30.90
Purchase #7	$187.71	12.810%	$211.7557	$211.76	$211.75	$211.80
7 purchase totals =	$632.20		$685.1705	$685.17	$685.15	$685.20