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	$156.52	13.619%	$177.8365	$177.84	$177.85	$177.80
Purchase #2	$51.92	7.107%	$55.61	$55.61	$55.60	$55.60
Purchase #3	$100.41	5.183%	$105.6143	$105.61	$105.60	$105.60
Purchase #4	$78.67	13.742%	$89.4808	$89.48	$89.50	$89.50
Purchase #5	$21.64	4.355%	$22.5824	$22.58	$22.60	$22.60
Purchase #6	$56.50	3.339%	$58.3865	$58.39	$58.40	$58.40
Purchase #7	$19.41	11.385%	$21.6198	$21.62	$21.60	$21.60
7 purchase totals =	$485.07		$531.1303	$531.13	$531.15	$531.10