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	$82.38	11.248%	$91.6461	$91.65	$91.65	$91.60
Purchase #2	$161.93	13.269%	$183.4165	$183.42	$183.40	$183.40
Purchase #3	$59.95	9.303%	$65.5271	$65.53	$65.55	$65.50
Purchase #4	$219.44	3.598%	$227.3355	$227.34	$227.35	$227.30
Purchase #5	$123.81	3.604%	$128.2721	$128.27	$128.25	$128.30
Purchase #6	$235.75	9.825%	$258.9124	$258.91	$258.90	$258.90
Purchase #7	$137.98	4.635%	$144.3754	$144.38	$144.40	$144.40
7 purchase totals =	$1,021.24		$1,099.4851	$1,099.50	$1,099.50	$1,099.40