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	$28.38	8.668%	$30.84	$30.84	$30.85	$30.80
Purchase #2	$84.49	13.181%	$95.6266	$95.63	$95.65	$95.60
Purchase #3	$148.84	5.835%	$157.5248	$157.52	$157.50	$157.50
Purchase #4	$185.37	5.757%	$196.0418	$196.04	$196.05	$196.00
Purchase #5	$40.77	13.213%	$46.1569	$46.16	$46.15	$46.20
Purchase #6	$28.95	11.774%	$32.3586	$32.36	$32.35	$32.40
Purchase #7	$30.33	7.462%	$32.5932	$32.59	$32.60	$32.60
7 purchase totals =	$547.13		$591.1419	$591.14	$591.15	$591.10