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	$70.39	8.417%	$76.3147	$76.31	$76.30	$76.30
Purchase #2	$158.93	9.192%	$173.5388	$173.54	$173.55	$173.50
Purchase #3	$102.31	9.417%	$111.9445	$111.94	$111.95	$111.90
Purchase #4	$175.78	9.630%	$192.7076	$192.71	$192.70	$192.70
Purchase #5	$11.61	10.698%	$12.852	$12.85	$12.85	$12.90
Purchase #6	$132.41	4.458%	$138.3128	$138.31	$138.30	$138.30
Purchase #7	$138.46	5.264%	$145.7485	$145.75	$145.75	$145.70
7 purchase totals =	$789.89		$851.4189	$851.41	$851.40	$851.30