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	$23.72	11.641%	$26.4812	$26.48	$26.50	$26.50
Purchase #2	$216.93	3.400%	$224.3056	$224.31	$224.30	$224.30
Purchase #3	$14.96	4.409%	$15.6196	$15.62	$15.60	$15.60
Purchase #4	$86.34	4.693%	$90.3919	$90.39	$90.40	$90.40
Purchase #5	$17.93	12.584%	$20.1863	$20.19	$20.20	$20.20
Purchase #6	$243.28	10.639%	$269.1626	$269.16	$269.15	$269.20
Purchase #7	$79.69	13.281%	$90.2736	$90.27	$90.25	$90.30
7 purchase totals =	$682.85		$736.4208	$736.42	$736.40	$736.50