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	$89.39	10.851%	$99.0897	$99.09	$99.10	$99.10
Purchase #2	$56.75	4.173%	$59.1182	$59.12	$59.10	$59.10
Purchase #3	$198.77	7.485%	$213.6479	$213.65	$213.65	$213.60
Purchase #4	$227.60	13.541%	$258.4193	$258.42	$258.40	$258.40
Purchase #5	$166.38	3.450%	$172.1201	$172.12	$172.10	$172.10
Purchase #6	$111.25	12.220%	$124.8448	$124.84	$124.85	$124.80
Purchase #7	$9.83	8.635%	$10.6788	$10.68	$10.70	$10.70
7 purchase totals =	$859.97		$937.9188	$937.92	$937.90	$937.80