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	$250.78	12.621%	$282.4309	$282.43	$282.45	$282.40
Purchase #2	$93.64	10.447%	$103.4226	$103.42	$103.40	$103.40
Purchase #3	$87.48	13.365%	$99.1717	$99.17	$99.15	$99.20
Purchase #4	$96.89	7.222%	$103.8874	$103.89	$103.90	$103.90
Purchase #5	$224.50	5.637%	$237.1551	$237.16	$237.15	$237.20
Purchase #6	$193.79	11.313%	$215.7135	$215.71	$215.70	$215.70
Purchase #7	$213.68	9.515%	$234.0117	$234.01	$234.00	$234.00
7 purchase totals =	$1,160.76		$1,275.7929	$1,275.79	$1,275.75	$1,275.80