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	$98.30	13.453%	$111.5243	$111.52	$111.50	$111.50
Purchase #2	$147.82	11.256%	$164.4586	$164.46	$164.45	$164.50
Purchase #3	$196.57	13.528%	$223.162	$223.16	$223.15	$223.20
Purchase #4	$199.97	7.256%	$214.4798	$214.48	$214.50	$214.50
Purchase #5	$99.35	12.556%	$111.8244	$111.82	$111.80	$111.80
Purchase #6	$148.91	10.182%	$164.072	$164.07	$164.05	$164.10
Purchase #7	$9.29	8.755%	$10.1033	$10.10	$10.10	$10.10
7 purchase totals =	$900.21		$999.6244	$999.61	$999.55	$999.70