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	$57.86	11.528%	$64.5301	$64.53	$64.55	$64.50
Purchase #2	$20.74	5.120%	$21.8019	$21.80	$21.80	$21.80
Purchase #3	$200.45	10.638%	$221.7739	$221.77	$221.75	$221.80
Purchase #4	$84.51	8.866%	$92.0027	$92.00	$92.00	$92.00
Purchase #5	$185.52	10.648%	$205.2742	$205.27	$205.25	$205.30
Purchase #6	$77.67	6.175%	$82.4661	$82.47	$82.45	$82.50
Purchase #7	$92.59	12.817%	$104.4573	$104.46	$104.45	$104.50
7 purchase totals =	$719.34		$792.3062	$792.30	$792.25	$792.40