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	$53.53	7.323%	$57.45	$57.45	$57.45	$57.50
Purchase #2	$110.71	9.295%	$121.0005	$121.00	$121.00	$121.00
Purchase #3	$80.72	11.214%	$89.7719	$89.77	$89.75	$89.80
Purchase #4	$22.86	5.740%	$24.1722	$24.17	$24.15	$24.20
Purchase #5	$45.61	4.175%	$47.5142	$47.51	$47.50	$47.50
Purchase #6	$197.27	13.752%	$224.3986	$224.40	$224.40	$224.40
Purchase #7	$151.32	11.406%	$168.5796	$168.58	$168.60	$168.60
7 purchase totals =	$662.02		$732.8870	$732.88	$732.85	$733.00