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	$75.69	9.284%	$82.7171	$82.72	$82.70	$82.70
Purchase #2	$108.40	5.193%	$114.0292	$114.03	$114.05	$114.00
Purchase #3	$144.60	3.627%	$149.8446	$149.84	$149.85	$149.80
Purchase #4	$241.43	5.821%	$255.4836	$255.48	$255.50	$255.50
Purchase #5	$180.52	13.681%	$205.2169	$205.22	$205.20	$205.20
Purchase #6	$204.54	12.850%	$230.8234	$230.82	$230.80	$230.80
Purchase #7	$247.72	9.609%	$271.5234	$271.52	$271.50	$271.50
7 purchase totals =	$1,202.90		$1,309.6382	$1,309.63	$1,309.60	$1,309.50