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	$124.84	5.853%	$132.1469	$132.15	$132.15	$132.10
Purchase #2	$91.58	6.229%	$97.2845	$97.28	$97.30	$97.30
Purchase #3	$217.61	9.768%	$238.8661	$238.87	$238.85	$238.90
Purchase #4	$53.85	9.804%	$59.1295	$59.13	$59.15	$59.10
Purchase #5	$39.81	11.513%	$44.3933	$44.39	$44.40	$44.40
Purchase #6	$15.30	7.583%	$16.4602	$16.46	$16.45	$16.50
Purchase #7	$62.59	13.698%	$71.1636	$71.16	$71.15	$71.20
7 purchase totals =	$605.58		$659.4441	$659.44	$659.45	$659.50