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	$169.32	8.485%	$183.6868	$183.69	$183.70	$183.70
Purchase #2	$137.33	5.747%	$145.2224	$145.22	$145.20	$145.20
Purchase #3	$92.67	11.649%	$103.4651	$103.47	$103.45	$103.50
Purchase #4	$198.31	11.616%	$221.3457	$221.35	$221.35	$221.30
Purchase #5	$127.64	10.336%	$140.8329	$140.83	$140.85	$140.80
Purchase #6	$10.86	4.413%	$11.3393	$11.34	$11.35	$11.30
Purchase #7	$56.57	8.719%	$61.5023	$61.50	$61.50	$61.50
7 purchase totals =	$792.70		$867.3945	$867.40	$867.40	$867.30