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	$48.74	11.230%	$54.2135	$54.21	$54.20	$54.20
Purchase #2	$111.54	10.738%	$123.5172	$123.52	$123.50	$123.50
Purchase #3	$57.71	5.398%	$60.8252	$60.83	$60.85	$60.80
Purchase #4	$75.26	4.319%	$78.5105	$78.51	$78.50	$78.50
Purchase #5	$100.39	4.633%	$105.0411	$105.04	$105.05	$105.00
Purchase #6	$47.26	10.779%	$52.3542	$52.35	$52.35	$52.40
Purchase #7	$105.39	8.231%	$114.0647	$114.06	$114.05	$114.10
7 purchase totals =	$546.29		$588.5264	$588.52	$588.50	$588.50