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	$159.46	12.509%	$179.4069	$179.41	$179.40	$179.40
Purchase #2	$242.62	13.593%	$275.5993	$275.60	$275.60	$275.60
Purchase #3	$113.83	4.835%	$119.3337	$119.33	$119.35	$119.30
Purchase #4	$199.97	4.766%	$209.5006	$209.50	$209.50	$209.50
Purchase #5	$210.91	11.346%	$234.8398	$234.84	$234.85	$234.80
Purchase #6	$33.56	13.219%	$37.9963	$38.00	$38.00	$38.00
Purchase #7	$216.27	11.651%	$241.4676	$241.47	$241.45	$241.50
7 purchase totals =	$1,176.62		$1,298.1442	$1,298.15	$1,298.15	$1,298.10