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	$54.33	12.259%	$60.9903	$60.99	$61.00	$61.00
Purchase #2	$224.31	10.732%	$248.3829	$248.38	$248.40	$248.40
Purchase #3	$182.28	4.545%	$190.5646	$190.56	$190.55	$190.60
Purchase #4	$133.91	8.714%	$145.5789	$145.58	$145.60	$145.60
Purchase #5	$19.26	12.436%	$21.6552	$21.66	$21.65	$21.70
Purchase #6	$72.48	13.344%	$82.1517	$82.15	$82.15	$82.20
Purchase #7	$37.50	6.704%	$40.014	$40.01	$40.00	$40.00
7 purchase totals =	$724.07		$789.3376	$789.33	$789.35	$789.50