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	$236.81	7.409%	$254.3553	$254.36	$254.35	$254.40
Purchase #2	$122.89	3.822%	$127.5869	$127.59	$127.60	$127.60
Purchase #3	$9.71	12.729%	$10.946	$10.95	$10.95	$10.90
Purchase #4	$65.38	10.556%	$72.2815	$72.28	$72.30	$72.30
Purchase #5	$192.90	12.543%	$217.0954	$217.10	$217.10	$217.10
Purchase #6	$63.54	4.474%	$66.3828	$66.38	$66.40	$66.40
Purchase #7	$37.48	8.198%	$40.5526	$40.55	$40.55	$40.60
7 purchase totals =	$728.71		$789.2005	$789.21	$789.25	$789.30