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	$138.46	4.315%	$144.4345	$144.43	$144.45	$144.40
Purchase #2	$242.72	4.844%	$254.4774	$254.48	$254.50	$254.50
Purchase #3	$43.37	12.747%	$48.8984	$48.90	$48.90	$48.90
Purchase #4	$49.75	4.800%	$52.138	$52.14	$52.15	$52.10
Purchase #5	$18.32	6.557%	$19.5212	$19.52	$19.50	$19.50
Purchase #6	$126.75	11.571%	$141.4162	$141.42	$141.40	$141.40
Purchase #7	$231.63	13.230%	$262.2746	$262.27	$262.25	$262.30
7 purchase totals =	$851.00		$923.1603	$923.16	$923.15	$923.10