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	$74.81	4.718%	$78.3395	$78.34	$78.35	$78.30
Purchase #2	$33.41	11.335%	$37.197	$37.20	$37.20	$37.20
Purchase #3	$126.25	9.566%	$138.3271	$138.33	$138.35	$138.30
Purchase #4	$117.56	10.828%	$130.2894	$130.29	$130.30	$130.30
Purchase #5	$164.83	6.415%	$175.4038	$175.40	$175.40	$175.40
Purchase #6	$36.26	10.697%	$40.1387	$40.14	$40.15	$40.10
Purchase #7	$81.31	7.871%	$87.7099	$87.71	$87.70	$87.70
7 purchase totals =	$634.43		$687.4054	$687.41	$687.45	$687.30