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	$91.55	8.804%	$99.6101	$99.61	$99.60	$99.60
Purchase #2	$124.36	13.489%	$141.1349	$141.13	$141.15	$141.10
Purchase #3	$198.72	12.533%	$223.6256	$223.63	$223.65	$223.60
Purchase #4	$139.78	4.388%	$145.9135	$145.91	$145.90	$145.90
Purchase #5	$205.61	6.159%	$218.2735	$218.27	$218.25	$218.30
Purchase #6	$213.74	12.152%	$239.7137	$239.71	$239.70	$239.70
Purchase #7	$116.65	13.338%	$132.2088	$132.21	$132.20	$132.20
7 purchase totals =	$1,090.41		$1,200.4801	$1,200.47	$1,200.45	$1,200.40