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	$137.54	12.525%	$154.7669	$154.77	$154.75	$154.80
Purchase #2	$52.75	7.735%	$56.8302	$56.83	$56.85	$56.80
Purchase #3	$74.73	11.728%	$83.4943	$83.49	$83.50	$83.50
Purchase #4	$57.78	3.453%	$59.7751	$59.78	$59.80	$59.80
Purchase #5	$247.60	8.748%	$269.26	$269.26	$269.25	$269.30
Purchase #6	$9.50	12.666%	$10.7033	$10.70	$10.70	$10.70
Purchase #7	$160.75	9.148%	$175.4554	$175.46	$175.45	$175.50
7 purchase totals =	$740.65		$810.2852	$810.29	$810.30	$810.40