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	$135.33	9.866%	$148.6817	$148.68	$148.70	$148.70
Purchase #2	$247.97	9.323%	$271.0882	$271.09	$271.10	$271.10
Purchase #3	$108.81	8.688%	$118.2634	$118.26	$118.25	$118.30
Purchase #4	$92.60	11.680%	$103.4157	$103.42	$103.40	$103.40
Purchase #5	$33.83	10.847%	$37.4995	$37.50	$37.50	$37.50
Purchase #6	$35.59	7.618%	$38.3012	$38.30	$38.30	$38.30
Purchase #7	$91.63	11.185%	$101.8788	$101.88	$101.90	$101.90
7 purchase totals =	$745.76		$819.1285	$819.13	$819.15	$819.20