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	$75.54	10.492%	$83.4657	$83.47	$83.45	$83.50
Purchase #2	$121.60	4.651%	$127.2556	$127.26	$127.25	$127.30
Purchase #3	$229.77	6.406%	$244.4891	$244.49	$244.50	$244.50
Purchase #4	$65.62	3.234%	$67.7422	$67.74	$67.75	$67.70
Purchase #5	$48.76	10.473%	$53.8666	$53.87	$53.85	$53.90
Purchase #6	$139.45	7.139%	$149.4053	$149.41	$149.40	$149.40
Purchase #7	$89.30	5.647%	$94.3428	$94.34	$94.35	$94.30
7 purchase totals =	$770.04		$820.5673	$820.58	$820.55	$820.60