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	$80.85	11.690%	$90.3014	$90.30	$90.30	$90.30
Purchase #2	$55.50	12.533%	$62.4558	$62.46	$62.45	$62.50
Purchase #3	$154.78	9.301%	$169.1761	$169.18	$169.20	$169.20
Purchase #4	$116.35	11.104%	$129.2695	$129.27	$129.25	$129.30
Purchase #5	$9.82	12.200%	$11.018	$11.02	$11.00	$11.00
Purchase #6	$50.56	13.276%	$57.2723	$57.27	$57.25	$57.30
Purchase #7	$46.71	4.501%	$48.8124	$48.81	$48.80	$48.80
7 purchase totals =	$514.57		$568.3055	$568.31	$568.25	$568.40