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	$90.31	11.536%	$100.7282	$100.73	$100.75	$100.70
Purchase #2	$250.31	9.690%	$274.565	$274.57	$274.55	$274.60
Purchase #3	$10.39	7.183%	$11.1363	$11.14	$11.15	$11.10
Purchase #4	$81.81	5.235%	$86.0928	$86.09	$86.10	$86.10
Purchase #5	$138.62	12.185%	$155.5108	$155.51	$155.50	$155.50
Purchase #6	$204.94	3.768%	$212.6621	$212.66	$212.65	$212.70
Purchase #7	$123.81	11.444%	$137.9788	$137.98	$138.00	$138.00
7 purchase totals =	$900.19		$978.6740	$978.68	$978.70	$978.70