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	$204.68	4.134%	$213.1415	$213.14	$213.15	$213.10
Purchase #2	$239.28	10.587%	$264.6126	$264.61	$264.60	$264.60
Purchase #3	$113.68	13.583%	$129.1212	$129.12	$129.10	$129.10
Purchase #4	$219.99	10.615%	$243.3419	$243.34	$243.35	$243.30
Purchase #5	$115.61	10.389%	$127.6207	$127.62	$127.60	$127.60
Purchase #6	$29.28	12.326%	$32.8891	$32.89	$32.90	$32.90
Purchase #7	$220.52	3.145%	$227.4554	$227.46	$227.45	$227.50
7 purchase totals =	$1,143.04		$1,238.1824	$1,238.18	$1,238.15	$1,238.10