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	$60.49	12.872%	$68.2763	$68.28	$68.30	$68.30
Purchase #2	$85.77	3.569%	$88.8311	$88.83	$88.85	$88.80
Purchase #3	$224.42	10.482%	$247.9437	$247.94	$247.95	$247.90
Purchase #4	$90.26	10.752%	$99.9648	$99.96	$99.95	$100.00
Purchase #5	$75.57	12.610%	$85.0994	$85.10	$85.10	$85.10
Purchase #6	$140.64	13.471%	$159.5856	$159.59	$159.60	$159.60
Purchase #7	$109.75	12.582%	$123.5587	$123.56	$123.55	$123.60
7 purchase totals =	$786.90		$873.2596	$873.26	$873.30	$873.30