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	$246.80	10.464%	$272.6252	$272.63	$272.65	$272.60
Purchase #2	$113.77	3.729%	$118.0125	$118.01	$118.00	$118.00
Purchase #3	$74.27	10.821%	$82.3068	$82.31	$82.30	$82.30
Purchase #4	$68.58	4.575%	$71.7175	$71.72	$71.70	$71.70
Purchase #5	$61.88	10.286%	$68.245	$68.25	$68.25	$68.20
Purchase #6	$120.71	11.475%	$134.5615	$134.56	$134.55	$134.60
Purchase #7	$20.51	6.172%	$21.7759	$21.78	$21.80	$21.80
7 purchase totals =	$706.52		$769.2444	$769.26	$769.25	$769.20