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	$198.51	12.531%	$223.3853	$223.39	$223.40	$223.40
Purchase #2	$147.38	5.691%	$155.7674	$155.77	$155.75	$155.80
Purchase #3	$207.45	7.278%	$222.5482	$222.55	$222.55	$222.50
Purchase #4	$238.48	9.199%	$260.4178	$260.42	$260.40	$260.40
Purchase #5	$37.31	7.871%	$40.2467	$40.25	$40.25	$40.20
Purchase #6	$132.54	8.552%	$143.8748	$143.87	$143.85	$143.90
Purchase #7	$53.51	12.427%	$60.1597	$60.16	$60.15	$60.20
7 purchase totals =	$1,015.18		$1,106.3999	$1,106.41	$1,106.35	$1,106.40