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	$49.40	10.745%	$54.708	$54.71	$54.70	$54.70
Purchase #2	$37.53	13.316%	$42.5275	$42.53	$42.55	$42.50
Purchase #3	$210.73	11.407%	$234.768	$234.77	$234.75	$234.80
Purchase #4	$60.61	3.753%	$62.8847	$62.88	$62.90	$62.90
Purchase #5	$55.29	9.720%	$60.6642	$60.66	$60.65	$60.70
Purchase #6	$151.43	6.228%	$160.8611	$160.86	$160.85	$160.90
Purchase #7	$61.81	10.742%	$68.4496	$68.45	$68.45	$68.40
7 purchase totals =	$626.80		$684.8631	$684.86	$684.85	$684.90