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	$81.37	10.160%	$89.6372	$89.64	$89.65	$89.60
Purchase #2	$28.52	5.298%	$30.031	$30.03	$30.05	$30.00
Purchase #3	$169.53	9.621%	$185.8405	$185.84	$185.85	$185.80
Purchase #4	$161.51	8.853%	$175.8085	$175.81	$175.80	$175.80
Purchase #5	$169.47	11.224%	$188.4913	$188.49	$188.50	$188.50
Purchase #6	$116.52	9.789%	$127.9261	$127.93	$127.95	$127.90
Purchase #7	$69.59	13.576%	$79.0375	$79.04	$79.05	$79.00
7 purchase totals =	$796.51		$876.7721	$876.78	$876.85	$876.60