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	$29.64	6.262%	$31.4961	$31.50	$31.50	$31.50
Purchase #2	$61.98	6.489%	$66.0019	$66.00	$66.00	$66.00
Purchase #3	$233.26	10.698%	$258.2142	$258.21	$258.20	$258.20
Purchase #4	$161.93	6.462%	$172.3939	$172.39	$172.40	$172.40
Purchase #5	$223.99	5.530%	$236.3766	$236.38	$236.40	$236.40
Purchase #6	$179.36	6.630%	$191.2516	$191.25	$191.25	$191.30
Purchase #7	$85.75	3.837%	$89.0402	$89.04	$89.05	$89.00
7 purchase totals =	$975.91		$1,044.7745	$1,044.77	$1,044.80	$1,044.80