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	$50.29	11.806%	$56.2272	$56.23	$56.25	$56.20
Purchase #2	$47.34	4.765%	$49.5958	$49.60	$49.60	$49.60
Purchase #3	$54.89	8.375%	$59.487	$59.49	$59.50	$59.50
Purchase #4	$200.50	10.250%	$221.0513	$221.05	$221.05	$221.10
Purchase #5	$100.63	6.149%	$106.8177	$106.82	$106.80	$106.80
Purchase #6	$46.86	3.850%	$48.6641	$48.66	$48.65	$48.70
Purchase #7	$30.60	11.281%	$34.052	$34.05	$34.05	$34.10
7 purchase totals =	$531.11		$575.8951	$575.90	$575.90	$576.00