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	$21.40	13.436%	$24.2753	$24.28	$24.30	$24.30
Purchase #2	$193.73	9.577%	$212.2835	$212.28	$212.30	$212.30
Purchase #3	$32.78	13.847%	$37.319	$37.32	$37.30	$37.30
Purchase #4	$247.98	12.609%	$279.2478	$279.25	$279.25	$279.20
Purchase #5	$72.57	9.490%	$79.4569	$79.46	$79.45	$79.50
Purchase #6	$220.63	10.401%	$243.5777	$243.58	$243.60	$243.60
Purchase #7	$91.97	8.690%	$99.9622	$99.96	$99.95	$100.00
7 purchase totals =	$881.06		$976.1224	$976.13	$976.15	$976.20