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	$120.34	8.486%	$130.5521	$130.55	$130.55	$130.60
Purchase #2	$61.65	9.315%	$67.3927	$67.39	$67.40	$67.40
Purchase #3	$191.71	7.204%	$205.5208	$205.52	$205.50	$205.50
Purchase #4	$172.35	5.756%	$182.2705	$182.27	$182.25	$182.30
Purchase #5	$200.70	7.570%	$215.893	$215.89	$215.90	$215.90
Purchase #6	$223.30	13.265%	$252.9207	$252.92	$252.90	$252.90
Purchase #7	$140.72	3.482%	$145.6199	$145.62	$145.60	$145.60
7 purchase totals =	$1,110.77		$1,200.1697	$1,200.16	$1,200.10	$1,200.20