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	$159.51	8.196%	$172.5834	$172.58	$172.60	$172.60
Purchase #2	$23.77	10.452%	$26.2544	$26.25	$26.25	$26.30
Purchase #3	$250.27	12.289%	$281.0257	$281.03	$281.05	$281.00
Purchase #4	$171.89	13.558%	$195.1948	$195.19	$195.20	$195.20
Purchase #5	$56.67	5.669%	$59.8826	$59.88	$59.90	$59.90
Purchase #6	$51.29	8.382%	$55.5891	$55.59	$55.60	$55.60
Purchase #7	$205.69	6.176%	$218.3934	$218.39	$218.40	$218.40
7 purchase totals =	$919.09		$1,008.9234	$1,008.91	$1,009.00	$1,009.00