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	$202.90	10.153%	$223.5004	$223.50	$223.50	$223.50
Purchase #2	$63.47	5.870%	$67.1957	$67.20	$67.20	$67.20
Purchase #3	$190.57	13.761%	$216.7943	$216.79	$216.80	$216.80
Purchase #4	$69.42	3.567%	$71.8962	$71.90	$71.90	$71.90
Purchase #5	$121.37	3.324%	$125.4043	$125.40	$125.40	$125.40
Purchase #6	$104.33	6.743%	$111.365	$111.37	$111.35	$111.40
Purchase #7	$158.60	9.212%	$173.2102	$173.21	$173.20	$173.20
7 purchase totals =	$910.66		$989.3661	$989.37	$989.35	$989.40