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	$95.61	10.663%	$105.8049	$105.80	$105.80	$105.80
Purchase #2	$108.63	13.844%	$123.6687	$123.67	$123.65	$123.70
Purchase #3	$123.82	5.479%	$130.6041	$130.60	$130.60	$130.60
Purchase #4	$67.69	4.630%	$70.824	$70.82	$70.80	$70.80
Purchase #5	$12.85	6.547%	$13.6913	$13.69	$13.70	$13.70
Purchase #6	$117.50	10.461%	$129.7917	$129.79	$129.80	$129.80
Purchase #7	$96.34	8.765%	$104.7842	$104.78	$104.80	$104.80
7 purchase totals =	$622.44		$679.1689	$679.15	$679.15	$679.20