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	$57.42	6.282%	$61.0271	$61.03	$61.05	$61.00
Purchase #2	$29.51	12.462%	$33.1875	$33.19	$33.20	$33.20
Purchase #3	$137.94	10.569%	$152.5189	$152.52	$152.50	$152.50
Purchase #4	$177.72	6.243%	$188.8151	$188.82	$188.80	$188.80
Purchase #5	$117.37	13.314%	$132.9966	$133.00	$133.00	$133.00
Purchase #6	$222.89	4.255%	$232.374	$232.37	$232.35	$232.40
Purchase #7	$213.74	7.815%	$230.4438	$230.44	$230.45	$230.40
7 purchase totals =	$956.59		$1,031.3630	$1,031.37	$1,031.35	$1,031.30