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	$135.25	8.536%	$146.7949	$146.79	$146.80	$146.80
Purchase #2	$75.54	12.737%	$85.1615	$85.16	$85.15	$85.20
Purchase #3	$121.27	10.311%	$133.7741	$133.77	$133.75	$133.80
Purchase #4	$158.89	4.140%	$165.468	$165.47	$165.45	$165.50
Purchase #5	$26.44	4.322%	$27.5827	$27.58	$27.60	$27.60
Purchase #6	$54.81	12.792%	$61.8213	$61.82	$61.80	$61.80
Purchase #7	$226.52	7.404%	$243.2915	$243.29	$243.30	$243.30
7 purchase totals =	$798.72		$863.8940	$863.88	$863.85	$864.00