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	$133.43	5.298%	$140.4991	$140.50	$140.50	$140.50
Purchase #2	$29.67	11.626%	$33.1194	$33.12	$33.10	$33.10
Purchase #3	$78.89	4.229%	$82.2263	$82.23	$82.25	$82.20
Purchase #4	$46.61	3.123%	$48.0656	$48.07	$48.05	$48.10
Purchase #5	$241.52	5.345%	$254.4292	$254.43	$254.45	$254.40
Purchase #6	$83.66	7.754%	$90.147	$90.15	$90.15	$90.10
Purchase #7	$238.34	7.753%	$256.8185	$256.82	$256.80	$256.80
7 purchase totals =	$852.12		$905.3051	$905.32	$905.30	$905.20