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	$65.58	7.669%	$70.6093	$70.61	$70.60	$70.60
Purchase #2	$132.59	13.520%	$150.5162	$150.52	$150.50	$150.50
Purchase #3	$59.42	8.706%	$64.5931	$64.59	$64.60	$64.60
Purchase #4	$236.34	11.497%	$263.512	$263.51	$263.50	$263.50
Purchase #5	$67.96	4.852%	$71.2574	$71.26	$71.25	$71.30
Purchase #6	$39.74	7.609%	$42.7638	$42.76	$42.75	$42.80
Purchase #7	$19.89	3.780%	$20.6418	$20.64	$20.65	$20.60
7 purchase totals =	$621.52		$683.8936	$683.89	$683.85	$683.90