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	$54.45	9.670%	$59.7153	$59.72	$59.70	$59.70
Purchase #2	$190.78	9.322%	$208.5645	$208.56	$208.55	$208.60
Purchase #3	$120.58	4.302%	$125.7674	$125.77	$125.75	$125.80
Purchase #4	$129.87	8.632%	$141.0804	$141.08	$141.10	$141.10
Purchase #5	$20.76	12.784%	$23.414	$23.41	$23.40	$23.40
Purchase #6	$227.56	12.145%	$255.1972	$255.20	$255.20	$255.20
Purchase #7	$80.72	11.185%	$89.7485	$89.75	$89.75	$89.70
7 purchase totals =	$824.72		$903.4873	$903.49	$903.45	$903.50