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	$240.35	13.281%	$272.2709	$272.27	$272.25	$272.30
Purchase #2	$158.60	10.229%	$174.8232	$174.82	$174.80	$174.80
Purchase #3	$109.74	3.139%	$113.1847	$113.18	$113.20	$113.20
Purchase #4	$108.81	12.591%	$122.5103	$122.51	$122.50	$122.50
Purchase #5	$44.53	11.113%	$49.4786	$49.48	$49.50	$49.50
Purchase #6	$85.61	4.471%	$89.4376	$89.44	$89.45	$89.40
Purchase #7	$123.57	3.657%	$128.089	$128.09	$128.10	$128.10
7 purchase totals =	$871.21		$949.7943	$949.79	$949.80	$949.80