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	$243.89	13.590%	$277.0347	$277.03	$277.05	$277.00
Purchase #2	$79.27	3.686%	$82.1919	$82.19	$82.20	$82.20
Purchase #3	$133.29	11.430%	$148.525	$148.53	$148.55	$148.50
Purchase #4	$153.72	11.117%	$170.8091	$170.81	$170.80	$170.80
Purchase #5	$154.97	7.471%	$166.5478	$166.55	$166.55	$166.50
Purchase #6	$159.57	8.142%	$172.5622	$172.56	$172.55	$172.60
Purchase #7	$132.55	12.345%	$148.9133	$148.91	$148.90	$148.90
7 purchase totals =	$1,057.26		$1,166.5840	$1,166.58	$1,166.60	$1,166.50