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	$34.71	13.773%	$39.4906	$39.49	$39.50	$39.50
Purchase #2	$117.25	3.140%	$120.9317	$120.93	$120.95	$120.90
Purchase #3	$78.77	4.692%	$82.4659	$82.47	$82.45	$82.50
Purchase #4	$49.52	9.222%	$54.0867	$54.09	$54.10	$54.10
Purchase #5	$129.96	9.578%	$142.4076	$142.41	$142.40	$142.40
Purchase #6	$81.78	3.229%	$84.4207	$84.42	$84.40	$84.40
Purchase #7	$37.64	5.581%	$39.7407	$39.74	$39.75	$39.70
7 purchase totals =	$529.63		$563.5439	$563.55	$563.55	$563.50