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	$33.82	4.138%	$35.2195	$35.22	$35.20	$35.20
Purchase #2	$146.35	6.411%	$155.7325	$155.73	$155.75	$155.70
Purchase #3	$29.76	9.276%	$32.5205	$32.52	$32.50	$32.50
Purchase #4	$108.43	10.104%	$119.3858	$119.39	$119.40	$119.40
Purchase #5	$123.91	8.298%	$134.1921	$134.19	$134.20	$134.20
Purchase #6	$192.83	12.463%	$216.8624	$216.86	$216.85	$216.90
Purchase #7	$205.28	8.409%	$222.542	$222.54	$222.55	$222.50
7 purchase totals =	$840.38		$916.4548	$916.45	$916.45	$916.40