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	$182.59	12.130%	$204.7382	$204.74	$204.75	$204.70
Purchase #2	$126.81	3.333%	$131.0366	$131.04	$131.05	$131.00
Purchase #3	$198.81	12.430%	$223.5221	$223.52	$223.50	$223.50
Purchase #4	$64.52	8.834%	$70.2197	$70.22	$70.20	$70.20
Purchase #5	$124.70	4.343%	$130.1157	$130.12	$130.10	$130.10
Purchase #6	$59.41	8.175%	$64.2668	$64.27	$64.25	$64.30
Purchase #7	$18.82	8.554%	$20.4299	$20.43	$20.45	$20.40
7 purchase totals =	$775.66		$844.3290	$844.34	$844.30	$844.20