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	$239.72	7.369%	$257.385	$257.39	$257.40	$257.40
Purchase #2	$82.40	11.158%	$91.5942	$91.59	$91.60	$91.60
Purchase #3	$150.78	10.289%	$166.2938	$166.29	$166.30	$166.30
Purchase #4	$152.53	8.526%	$165.5347	$165.53	$165.55	$165.50
Purchase #5	$129.75	7.485%	$139.4618	$139.46	$139.45	$139.50
Purchase #6	$23.72	4.121%	$24.6975	$24.70	$24.70	$24.70
Purchase #7	$81.59	5.290%	$85.9061	$85.91	$85.90	$85.90
7 purchase totals =	$860.49		$930.8731	$930.87	$930.90	$930.90