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	$121.87	11.671%	$136.0934	$136.09	$136.10	$136.10
Purchase #2	$149.52	7.626%	$160.9224	$160.92	$160.90	$160.90
Purchase #3	$18.59	5.414%	$19.5965	$19.60	$19.60	$19.60
Purchase #4	$235.61	12.804%	$265.7775	$265.78	$265.80	$265.80
Purchase #5	$101.69	4.514%	$106.2803	$106.28	$106.30	$106.30
Purchase #6	$205.77	12.718%	$231.9398	$231.94	$231.95	$231.90
Purchase #7	$56.31	6.447%	$59.9403	$59.94	$59.95	$59.90
7 purchase totals =	$889.36		$980.5502	$980.55	$980.60	$980.50