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	$231.79	10.821%	$256.872	$256.87	$256.85	$256.90
Purchase #2	$137.39	11.104%	$152.6458	$152.65	$152.65	$152.60
Purchase #3	$51.73	7.467%	$55.5927	$55.59	$55.60	$55.60
Purchase #4	$163.97	12.687%	$184.7729	$184.77	$184.75	$184.80
Purchase #5	$80.99	11.346%	$90.1791	$90.18	$90.20	$90.20
Purchase #6	$24.86	11.659%	$27.7584	$27.76	$27.75	$27.80
Purchase #7	$23.38	4.566%	$24.4475	$24.45	$24.45	$24.40
7 purchase totals =	$714.11		$792.2684	$792.27	$792.25	$792.30