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	$67.98	4.300%	$70.9031	$70.90	$70.90	$70.90
Purchase #2	$244.75	5.605%	$258.4682	$258.47	$258.45	$258.50
Purchase #3	$27.85	8.834%	$30.3103	$30.31	$30.30	$30.30
Purchase #4	$40.90	10.792%	$45.3139	$45.31	$45.30	$45.30
Purchase #5	$113.85	6.147%	$120.8484	$120.85	$120.85	$120.80
Purchase #6	$27.89	10.537%	$30.8288	$30.83	$30.85	$30.80
Purchase #7	$248.50	12.116%	$278.6083	$278.61	$278.60	$278.60
7 purchase totals =	$771.72		$835.2810	$835.28	$835.25	$835.20