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	$242.49	13.835%	$276.0385	$276.04	$276.05	$276.00
Purchase #2	$82.75	13.670%	$94.0619	$94.06	$94.05	$94.10
Purchase #3	$219.37	10.230%	$241.8116	$241.81	$241.80	$241.80
Purchase #4	$33.37	13.660%	$37.9283	$37.93	$37.95	$37.90
Purchase #5	$72.94	7.191%	$78.1851	$78.19	$78.20	$78.20
Purchase #6	$143.74	11.548%	$160.3391	$160.34	$160.35	$160.30
Purchase #7	$79.70	10.697%	$88.2255	$88.23	$88.25	$88.20
7 purchase totals =	$874.36		$976.5900	$976.60	$976.65	$976.50