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	$108.93	12.172%	$122.189	$122.19	$122.20	$122.20
Purchase #2	$154.82	11.621%	$172.8116	$172.81	$172.80	$172.80
Purchase #3	$206.38	12.822%	$232.842	$232.84	$232.85	$232.80
Purchase #4	$40.90	4.150%	$42.5974	$42.60	$42.60	$42.60
Purchase #5	$160.71	5.525%	$169.5892	$169.59	$169.60	$169.60
Purchase #6	$39.94	7.840%	$43.0713	$43.07	$43.05	$43.10
Purchase #7	$63.83	3.137%	$65.8323	$65.83	$65.85	$65.80
7 purchase totals =	$775.51		$848.9328	$848.93	$848.95	$848.90