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	$101.50	10.256%	$111.9098	$111.91	$111.90	$111.90
Purchase #2	$38.60	3.126%	$39.8066	$39.81	$39.80	$39.80
Purchase #3	$94.84	8.180%	$102.5979	$102.60	$102.60	$102.60
Purchase #4	$154.80	3.753%	$160.6096	$160.61	$160.60	$160.60
Purchase #5	$118.44	10.485%	$130.8584	$130.86	$130.85	$130.90
Purchase #6	$249.99	11.250%	$278.1139	$278.11	$278.10	$278.10
Purchase #7	$72.66	6.454%	$77.3495	$77.35	$77.35	$77.30
7 purchase totals =	$830.83		$901.2457	$901.25	$901.20	$901.20