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	$221.90	7.655%	$238.8864	$238.89	$238.90	$238.90
Purchase #2	$72.50	10.544%	$80.1444	$80.14	$80.15	$80.10
Purchase #3	$130.43	8.155%	$141.0666	$141.07	$141.05	$141.10
Purchase #4	$152.56	13.474%	$173.1159	$173.12	$173.10	$173.10
Purchase #5	$241.60	12.642%	$272.1431	$272.14	$272.15	$272.10
Purchase #6	$100.91	10.198%	$111.2008	$111.20	$111.20	$111.20
Purchase #7	$150.81	10.673%	$166.906	$166.91	$166.90	$166.90
7 purchase totals =	$1,070.71		$1,183.4632	$1,183.47	$1,183.45	$1,183.40