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	$80.65	13.739%	$91.7305	$91.73	$91.75	$91.70
Purchase #2	$21.67	12.627%	$24.4063	$24.41	$24.40	$24.40
Purchase #3	$197.46	13.331%	$223.7834	$223.78	$223.80	$223.80
Purchase #4	$222.67	12.145%	$249.7133	$249.71	$249.70	$249.70
Purchase #5	$145.61	8.716%	$158.3014	$158.30	$158.30	$158.30
Purchase #6	$191.62	13.557%	$217.5979	$217.60	$217.60	$217.60
Purchase #7	$108.73	13.395%	$123.2944	$123.29	$123.30	$123.30
7 purchase totals =	$968.41		$1,088.8272	$1,088.82	$1,088.85	$1,088.80