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	$39.99	6.146%	$42.4478	$42.45	$42.45	$42.40
Purchase #2	$126.62	4.476%	$132.2875	$132.29	$132.30	$132.30
Purchase #3	$84.96	7.399%	$91.2462	$91.25	$91.25	$91.20
Purchase #4	$34.88	8.584%	$37.8741	$37.87	$37.85	$37.90
Purchase #5	$59.37	10.206%	$65.4293	$65.43	$65.45	$65.40
Purchase #6	$14.55	7.842%	$15.691	$15.69	$15.70	$15.70
Purchase #7	$99.73	3.799%	$103.5187	$103.52	$103.50	$103.50
7 purchase totals =	$460.10		$488.4946	$488.50	$488.50	$488.40