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	$193.64	10.401%	$213.7805	$213.78	$213.80	$213.80
Purchase #2	$96.36	13.342%	$109.2164	$109.22	$109.20	$109.20
Purchase #3	$34.44	3.503%	$35.6464	$35.65	$35.65	$35.60
Purchase #4	$31.92	4.257%	$33.2788	$33.28	$33.30	$33.30
Purchase #5	$205.85	10.657%	$227.7874	$227.79	$227.80	$227.80
Purchase #6	$153.60	5.713%	$162.3752	$162.38	$162.40	$162.40
Purchase #7	$35.25	7.455%	$37.8779	$37.88	$37.90	$37.90
7 purchase totals =	$751.06		$819.9626	$819.98	$820.05	$820.00