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	$225.59	3.340%	$233.1247	$233.12	$233.10	$233.10
Purchase #2	$131.26	11.859%	$146.8261	$146.83	$146.85	$146.80
Purchase #3	$170.79	7.351%	$183.3448	$183.34	$183.35	$183.30
Purchase #4	$137.78	7.720%	$148.4166	$148.42	$148.40	$148.40
Purchase #5	$107.93	10.575%	$119.3436	$119.34	$119.35	$119.30
Purchase #6	$131.72	4.262%	$137.3339	$137.33	$137.35	$137.30
Purchase #7	$63.77	5.344%	$67.1779	$67.18	$67.20	$67.20
7 purchase totals =	$968.84		$1,035.5676	$1,035.56	$1,035.60	$1,035.40