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	$211.74	9.386%	$231.6139	$231.61	$231.60	$231.60
Purchase #2	$29.74	13.736%	$33.8251	$33.83	$33.85	$33.80
Purchase #3	$50.72	13.602%	$57.6189	$57.62	$57.60	$57.60
Purchase #4	$200.78	3.757%	$208.3233	$208.32	$208.30	$208.30
Purchase #5	$78.75	4.246%	$82.0937	$82.09	$82.10	$82.10
Purchase #6	$161.87	12.542%	$182.1717	$182.17	$182.15	$182.20
Purchase #7	$149.47	7.407%	$160.5412	$160.54	$160.55	$160.50
7 purchase totals =	$883.07		$956.1878	$956.18	$956.15	$956.10