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	$35.77	8.726%	$38.8913	$38.89	$38.90	$38.90
Purchase #2	$43.83	7.404%	$47.0752	$47.08	$47.10	$47.10
Purchase #3	$195.93	4.610%	$204.9624	$204.96	$204.95	$205.00
Purchase #4	$169.59	9.434%	$185.5891	$185.59	$185.60	$185.60
Purchase #5	$74.61	3.394%	$77.1423	$77.14	$77.15	$77.10
Purchase #6	$50.32	6.855%	$53.7694	$53.77	$53.75	$53.80
Purchase #7	$149.73	3.461%	$154.9122	$154.91	$154.90	$154.90
7 purchase totals =	$719.78		$762.3419	$762.34	$762.35	$762.40