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	$72.44	12.496%	$81.4921	$81.49	$81.50	$81.50
Purchase #2	$154.44	13.429%	$175.1797	$175.18	$175.20	$175.20
Purchase #3	$239.65	13.336%	$271.6097	$271.61	$271.60	$271.60
Purchase #4	$112.50	9.665%	$123.3731	$123.37	$123.35	$123.40
Purchase #5	$153.73	12.174%	$172.4451	$172.45	$172.45	$172.40
Purchase #6	$225.60	4.177%	$235.0233	$235.02	$235.00	$235.00
Purchase #7	$220.53	4.107%	$229.5872	$229.59	$229.60	$229.60
7 purchase totals =	$1,178.89		$1,288.7102	$1,288.71	$1,288.70	$1,288.70