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	$12.53	10.325%	$13.8237	$13.82	$13.80	$13.80
Purchase #2	$73.27	8.116%	$79.2166	$79.22	$79.20	$79.20
Purchase #3	$200.52	12.616%	$225.8176	$225.82	$225.80	$225.80
Purchase #4	$130.45	12.734%	$147.0615	$147.06	$147.05	$147.10
Purchase #5	$65.50	7.656%	$70.5147	$70.51	$70.50	$70.50
Purchase #6	$148.96	13.139%	$168.5319	$168.53	$168.55	$168.50
Purchase #7	$79.94	13.603%	$90.8142	$90.81	$90.80	$90.80
7 purchase totals =	$711.17		$795.7802	$795.77	$795.70	$795.70