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	$153.96	4.260%	$160.5187	$160.52	$160.50	$160.50
Purchase #2	$194.32	7.714%	$209.3098	$209.31	$209.30	$209.30
Purchase #3	$80.74	9.788%	$88.6428	$88.64	$88.65	$88.60
Purchase #4	$6.81	4.379%	$7.1082	$7.11	$7.10	$7.10
Purchase #5	$52.97	12.403%	$59.5399	$59.54	$59.55	$59.50
Purchase #6	$46.91	7.244%	$50.3082	$50.31	$50.30	$50.30
Purchase #7	$78.28	11.487%	$87.272	$87.27	$87.25	$87.30
7 purchase totals =	$613.99		$662.6996	$662.70	$662.65	$662.60