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	$57.71	3.810%	$59.9088	$59.91	$59.90	$59.90
Purchase #2	$32.58	10.763%	$36.0866	$36.09	$36.10	$36.10
Purchase #3	$45.68	13.764%	$51.9674	$51.97	$51.95	$52.00
Purchase #4	$67.80	7.295%	$72.746	$72.75	$72.75	$72.70
Purchase #5	$14.45	5.276%	$15.2124	$15.21	$15.20	$15.20
Purchase #6	$167.76	10.356%	$185.1332	$185.13	$185.15	$185.10
Purchase #7	$134.64	11.339%	$149.9068	$149.91	$149.90	$149.90
7 purchase totals =	$520.62		$570.9612	$570.97	$570.95	$570.90