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	$40.67	4.324%	$42.4286	$42.43	$42.45	$42.40
Purchase #2	$111.30	12.830%	$125.5798	$125.58	$125.60	$125.60
Purchase #3	$167.64	10.302%	$184.9103	$184.91	$184.90	$184.90
Purchase #4	$77.54	7.237%	$83.1516	$83.15	$83.15	$83.20
Purchase #5	$167.26	3.141%	$172.5136	$172.51	$172.50	$172.50
Purchase #6	$197.50	5.302%	$207.9715	$207.97	$207.95	$208.00
Purchase #7	$192.85	6.449%	$205.2869	$205.29	$205.30	$205.30
7 purchase totals =	$954.76		$1,021.8423	$1,021.84	$1,021.85	$1,021.90