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	$69.37	13.683%	$78.8619	$78.86	$78.85	$78.90
Purchase #2	$108.45	9.613%	$118.8753	$118.88	$118.90	$118.90
Purchase #3	$236.58	11.709%	$264.2812	$264.28	$264.30	$264.30
Purchase #4	$213.41	11.808%	$238.6095	$238.61	$238.60	$238.60
Purchase #5	$166.80	3.228%	$172.1843	$172.18	$172.20	$172.20
Purchase #6	$194.38	12.220%	$218.1332	$218.13	$218.15	$218.10
Purchase #7	$88.83	3.754%	$92.1647	$92.16	$92.15	$92.20
7 purchase totals =	$1,077.82		$1,183.1101	$1,183.10	$1,183.15	$1,183.20