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	$25.33	13.295%	$28.6976	$28.70	$28.70	$28.70
Purchase #2	$19.64	10.492%	$21.7006	$21.70	$21.70	$21.70
Purchase #3	$13.90	9.560%	$15.2288	$15.23	$15.25	$15.20
Purchase #4	$155.50	10.723%	$172.1743	$172.17	$172.15	$172.20
Purchase #5	$180.56	6.369%	$192.0599	$192.06	$192.05	$192.10
Purchase #6	$163.26	13.834%	$185.8454	$185.85	$185.85	$185.80
Purchase #7	$200.77	10.484%	$221.8187	$221.82	$221.80	$221.80
7 purchase totals =	$758.96		$837.5253	$837.53	$837.50	$837.50