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	$124.73	5.143%	$131.1449	$131.14	$131.15	$131.10
Purchase #2	$249.52	9.194%	$272.4609	$272.46	$272.45	$272.50
Purchase #3	$167.71	12.536%	$188.7341	$188.73	$188.75	$188.70
Purchase #4	$61.32	5.435%	$64.6527	$64.65	$64.65	$64.70
Purchase #5	$142.90	13.406%	$162.0572	$162.06	$162.05	$162.10
Purchase #6	$9.60	7.376%	$10.3081	$10.31	$10.30	$10.30
Purchase #7	$35.45	10.750%	$39.2609	$39.26	$39.25	$39.30
7 purchase totals =	$791.23		$868.6188	$868.61	$868.60	$868.70