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	$19.43	4.255%	$20.2567	$20.26	$20.25	$20.30
Purchase #2	$248.35	6.243%	$263.8545	$263.85	$263.85	$263.90
Purchase #3	$59.73	10.162%	$65.7998	$65.80	$65.80	$65.80
Purchase #4	$132.40	4.464%	$138.3103	$138.31	$138.30	$138.30
Purchase #5	$145.62	5.309%	$153.351	$153.35	$153.35	$153.40
Purchase #6	$19.39	4.681%	$20.2976	$20.30	$20.30	$20.30
Purchase #7	$174.43	7.791%	$188.0198	$188.02	$188.00	$188.00
7 purchase totals =	$799.35		$849.8897	$849.89	$849.85	$850.00