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	$124.47	5.468%	$131.276	$131.28	$131.30	$131.30
Purchase #2	$176.48	8.866%	$192.1267	$192.13	$192.15	$192.10
Purchase #3	$147.46	12.381%	$165.717	$165.72	$165.70	$165.70
Purchase #4	$74.33	11.181%	$82.6408	$82.64	$82.65	$82.60
Purchase #5	$157.45	5.264%	$165.7382	$165.74	$165.75	$165.70
Purchase #6	$18.85	12.399%	$21.1872	$21.19	$21.20	$21.20
Purchase #7	$208.89	7.716%	$225.008	$225.01	$225.00	$225.00
7 purchase totals =	$907.93		$983.6939	$983.71	$983.75	$983.60