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	$11.27	11.116%	$12.5228	$12.52	$12.50	$12.50
Purchase #2	$240.59	13.372%	$272.7617	$272.76	$272.75	$272.80
Purchase #3	$129.59	7.393%	$139.1706	$139.17	$139.15	$139.20
Purchase #4	$153.45	3.772%	$159.2381	$159.24	$159.25	$159.20
Purchase #5	$78.59	3.447%	$81.299	$81.30	$81.30	$81.30
Purchase #6	$35.79	5.822%	$37.8737	$37.87	$37.85	$37.90
Purchase #7	$149.54	12.509%	$168.246	$168.25	$168.25	$168.20
7 purchase totals =	$798.82		$871.1119	$871.11	$871.05	$871.10