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	$149.32	12.445%	$167.9029	$167.90	$167.90	$167.90
Purchase #2	$62.81	6.140%	$66.6665	$66.67	$66.65	$66.70
Purchase #3	$18.87	8.631%	$20.4987	$20.50	$20.50	$20.50
Purchase #4	$229.72	9.278%	$251.0334	$251.03	$251.05	$251.00
Purchase #5	$89.37	5.566%	$94.3443	$94.34	$94.35	$94.30
Purchase #6	$54.42	5.187%	$57.2428	$57.24	$57.25	$57.20
Purchase #7	$244.45	10.743%	$270.7113	$270.71	$270.70	$270.70
7 purchase totals =	$848.96		$928.3999	$928.39	$928.40	$928.30