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	$23.36	9.766%	$25.6413	$25.64	$25.65	$25.60
Purchase #2	$108.29	5.518%	$114.2654	$114.27	$114.25	$114.30
Purchase #3	$123.60	12.667%	$139.2564	$139.26	$139.25	$139.30
Purchase #4	$231.43	4.673%	$242.2447	$242.24	$242.25	$242.20
Purchase #5	$70.93	9.775%	$77.8634	$77.86	$77.85	$77.90
Purchase #6	$57.45	7.719%	$61.8846	$61.88	$61.90	$61.90
Purchase #7	$97.54	3.273%	$100.7325	$100.73	$100.75	$100.70
7 purchase totals =	$712.60		$761.8883	$761.88	$761.90	$761.90