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	$241.59	6.511%	$257.3199	$257.32	$257.30	$257.30
Purchase #2	$133.75	10.855%	$148.2686	$148.27	$148.25	$148.30
Purchase #3	$18.89	7.777%	$20.3591	$20.36	$20.35	$20.40
Purchase #4	$92.67	8.552%	$100.5951	$100.60	$100.60	$100.60
Purchase #5	$233.55	5.127%	$245.5241	$245.52	$245.50	$245.50
Purchase #6	$160.36	13.650%	$182.2491	$182.25	$182.25	$182.20
Purchase #7	$22.36	6.544%	$23.8232	$23.82	$23.80	$23.80
7 purchase totals =	$903.17		$978.1391	$978.14	$978.05	$978.10