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	$83.59	6.346%	$88.8946	$88.89	$88.90	$88.90
Purchase #2	$17.65	4.210%	$18.3931	$18.39	$18.40	$18.40
Purchase #3	$154.55	3.831%	$160.4708	$160.47	$160.45	$160.50
Purchase #4	$80.29	12.788%	$90.5575	$90.56	$90.55	$90.60
Purchase #5	$123.43	7.284%	$132.4206	$132.42	$132.40	$132.40
Purchase #6	$197.66	9.506%	$216.4496	$216.45	$216.45	$216.40
Purchase #7	$236.87	7.627%	$254.9361	$254.94	$254.95	$254.90
7 purchase totals =	$894.04		$962.1223	$962.12	$962.10	$962.10