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	$39.71	4.738%	$41.5915	$41.59	$41.60	$41.60
Purchase #2	$155.97	10.586%	$172.481	$172.48	$172.50	$172.50
Purchase #3	$140.36	10.245%	$154.7399	$154.74	$154.75	$154.70
Purchase #4	$120.87	10.445%	$133.4949	$133.49	$133.50	$133.50
Purchase #5	$221.61	4.236%	$230.9974	$231.00	$231.00	$231.00
Purchase #6	$113.87	8.487%	$123.5341	$123.53	$123.55	$123.50
Purchase #7	$219.33	4.310%	$228.7831	$228.78	$228.80	$228.80
7 purchase totals =	$1,011.72		$1,085.6219	$1,085.61	$1,085.70	$1,085.60