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	$16.95	3.159%	$17.4855	$17.49	$17.50	$17.50
Purchase #2	$242.76	13.387%	$275.2583	$275.26	$275.25	$275.30
Purchase #3	$114.57	4.873%	$120.153	$120.15	$120.15	$120.20
Purchase #4	$9.57	7.236%	$10.2625	$10.26	$10.25	$10.30
Purchase #5	$32.72	13.549%	$37.1532	$37.15	$37.15	$37.20
Purchase #6	$28.72	13.282%	$32.5346	$32.53	$32.55	$32.50
Purchase #7	$17.96	4.229%	$18.7195	$18.72	$18.70	$18.70
7 purchase totals =	$463.25		$511.5666	$511.56	$511.55	$511.70