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	$176.33	7.189%	$189.0064	$189.01	$189.00	$189.00
Purchase #2	$123.94	12.453%	$139.3742	$139.37	$139.35	$139.40
Purchase #3	$172.27	8.167%	$186.3393	$186.34	$186.35	$186.30
Purchase #4	$233.59	9.332%	$255.3886	$255.39	$255.40	$255.40
Purchase #5	$148.59	7.522%	$159.7669	$159.77	$159.75	$159.80
Purchase #6	$234.50	10.511%	$259.1483	$259.15	$259.15	$259.10
Purchase #7	$143.97	10.867%	$159.6152	$159.62	$159.60	$159.60
7 purchase totals =	$1,233.19		$1,348.6389	$1,348.65	$1,348.60	$1,348.60