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	$189.89	11.764%	$212.2287	$212.23	$212.25	$212.20
Purchase #2	$18.72	8.359%	$20.2848	$20.28	$20.30	$20.30
Purchase #3	$59.33	12.791%	$66.9189	$66.92	$66.90	$66.90
Purchase #4	$167.65	13.636%	$190.5108	$190.51	$190.50	$190.50
Purchase #5	$189.25	10.643%	$209.3919	$209.39	$209.40	$209.40
Purchase #6	$51.33	3.146%	$52.9448	$52.94	$52.95	$52.90
Purchase #7	$161.64	3.720%	$167.653	$167.65	$167.65	$167.70
7 purchase totals =	$837.81		$919.9329	$919.92	$919.95	$919.90