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	$151.65	13.737%	$172.4822	$172.48	$172.50	$172.50
Purchase #2	$93.31	7.375%	$100.1916	$100.19	$100.20	$100.20
Purchase #3	$38.56	6.475%	$41.0568	$41.06	$41.05	$41.10
Purchase #4	$104.85	10.845%	$116.221	$116.22	$116.20	$116.20
Purchase #5	$30.80	12.406%	$34.621	$34.62	$34.60	$34.60
Purchase #6	$185.66	4.427%	$193.8792	$193.88	$193.90	$193.90
Purchase #7	$123.27	10.592%	$136.3268	$136.33	$136.35	$136.30
7 purchase totals =	$728.10		$794.7786	$794.78	$794.80	$794.80