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	$146.93	8.786%	$159.8393	$159.84	$159.85	$159.80
Purchase #2	$122.26	8.611%	$132.7878	$132.79	$132.80	$132.80
Purchase #3	$55.33	7.692%	$59.586	$59.59	$59.60	$59.60
Purchase #4	$99.52	9.843%	$109.3158	$109.32	$109.30	$109.30
Purchase #5	$65.26	8.699%	$70.937	$70.94	$70.95	$70.90
Purchase #6	$60.66	8.479%	$65.8034	$65.80	$65.80	$65.80
Purchase #7	$90.94	3.535%	$94.1547	$94.15	$94.15	$94.20
7 purchase totals =	$640.90		$692.4240	$692.43	$692.45	$692.40