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	$145.34	9.113%	$158.5848	$158.58	$158.60	$158.60
Purchase #2	$101.82	6.216%	$108.1491	$108.15	$108.15	$108.10
Purchase #3	$221.78	8.597%	$240.8464	$240.85	$240.85	$240.80
Purchase #4	$10.71	5.759%	$11.3268	$11.33	$11.35	$11.30
Purchase #5	$149.48	10.192%	$164.715	$164.72	$164.70	$164.70
Purchase #6	$175.77	4.864%	$184.3195	$184.32	$184.30	$184.30
Purchase #7	$113.92	11.332%	$126.8294	$126.83	$126.85	$126.80
7 purchase totals =	$918.82		$994.7710	$994.78	$994.80	$994.60