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	$245.35	3.375%	$253.6306	$253.63	$253.65	$253.60
Purchase #2	$111.40	11.140%	$123.81	$123.81	$123.80	$123.80
Purchase #3	$20.57	9.739%	$22.5733	$22.57	$22.55	$22.60
Purchase #4	$250.71	12.723%	$282.6078	$282.61	$282.60	$282.60
Purchase #5	$172.75	7.609%	$185.8945	$185.89	$185.90	$185.90
Purchase #6	$163.46	4.105%	$170.17	$170.17	$170.15	$170.20
Purchase #7	$37.35	5.335%	$39.3426	$39.34	$39.35	$39.30
7 purchase totals =	$1,001.59		$1,078.0288	$1,078.02	$1,078.00	$1,078.00