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	$96.32	7.298%	$103.3494	$103.35	$103.35	$103.30
Purchase #2	$50.59	13.620%	$57.4804	$57.48	$57.50	$57.50
Purchase #3	$50.49	3.444%	$52.2289	$52.23	$52.25	$52.20
Purchase #4	$122.94	9.364%	$134.4521	$134.45	$134.45	$134.50
Purchase #5	$75.67	12.500%	$85.1288	$85.13	$85.15	$85.10
Purchase #6	$54.61	8.494%	$59.2486	$59.25	$59.25	$59.20
Purchase #7	$105.77	4.680%	$110.72	$110.72	$110.70	$110.70
7 purchase totals =	$556.39		$602.6082	$602.61	$602.65	$602.50