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	$185.71	10.471%	$205.1557	$205.16	$205.15	$205.20
Purchase #2	$96.88	6.628%	$103.3012	$103.30	$103.30	$103.30
Purchase #3	$243.39	13.355%	$275.8947	$275.89	$275.90	$275.90
Purchase #4	$139.49	3.309%	$144.1057	$144.11	$144.10	$144.10
Purchase #5	$59.38	12.545%	$66.8292	$66.83	$66.85	$66.80
Purchase #6	$128.45	6.618%	$136.9508	$136.95	$136.95	$137.00
Purchase #7	$130.93	11.595%	$146.1113	$146.11	$146.10	$146.10
7 purchase totals =	$984.23		$1,078.3486	$1,078.35	$1,078.35	$1,078.40