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	$37.61	5.782%	$39.7846	$39.78	$39.80	$39.80
Purchase #2	$98.29	3.296%	$101.5296	$101.53	$101.55	$101.50
Purchase #3	$47.65	9.800%	$52.3197	$52.32	$52.30	$52.30
Purchase #4	$138.73	4.183%	$144.5331	$144.53	$144.55	$144.50
Purchase #5	$36.34	12.164%	$40.7604	$40.76	$40.75	$40.80
Purchase #6	$244.38	4.610%	$255.6459	$255.65	$255.65	$255.60
Purchase #7	$17.25	10.568%	$19.073	$19.07	$19.05	$19.10
7 purchase totals =	$620.25		$653.6463	$653.64	$653.65	$653.60