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	$18.54	4.469%	$19.3686	$19.37	$19.35	$19.40
Purchase #2	$107.87	3.141%	$111.2582	$111.26	$111.25	$111.30
Purchase #3	$86.59	13.521%	$98.2978	$98.30	$98.30	$98.30
Purchase #4	$31.40	9.353%	$34.3368	$34.34	$34.35	$34.30
Purchase #5	$31.89	3.282%	$32.9366	$32.94	$32.95	$32.90
Purchase #6	$234.95	5.253%	$247.2919	$247.29	$247.30	$247.30
Purchase #7	$54.44	6.769%	$58.125	$58.13	$58.15	$58.10
7 purchase totals =	$565.68		$601.6149	$601.63	$601.65	$601.60