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	$52.78	6.587%	$56.2566	$56.26	$56.25	$56.30
Purchase #2	$174.54	10.854%	$193.4846	$193.48	$193.50	$193.50
Purchase #3	$180.50	11.140%	$200.6077	$200.61	$200.60	$200.60
Purchase #4	$153.25	11.129%	$170.3052	$170.31	$170.30	$170.30
Purchase #5	$114.43	7.698%	$123.2388	$123.24	$123.25	$123.20
Purchase #6	$50.40	12.827%	$56.8648	$56.86	$56.85	$56.90
Purchase #7	$70.62	4.561%	$73.841	$73.84	$73.85	$73.80
7 purchase totals =	$796.52		$874.5987	$874.60	$874.60	$874.60