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	$23.66	11.680%	$26.4235	$26.42	$26.40	$26.40
Purchase #2	$223.59	6.824%	$238.8478	$238.85	$238.85	$238.80
Purchase #3	$169.63	12.222%	$190.3622	$190.36	$190.35	$190.40
Purchase #4	$13.95	7.468%	$14.9918	$14.99	$15.00	$15.00
Purchase #5	$73.78	11.527%	$82.2846	$82.28	$82.30	$82.30
Purchase #6	$167.33	4.852%	$175.4489	$175.45	$175.45	$175.40
Purchase #7	$90.99	9.412%	$99.554	$99.55	$99.55	$99.60
7 purchase totals =	$762.93		$827.9128	$827.90	$827.90	$827.90