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	$18.94	12.366%	$21.2821	$21.28	$21.30	$21.30
Purchase #2	$75.68	7.723%	$81.5248	$81.52	$81.50	$81.50
Purchase #3	$92.25	11.658%	$103.0045	$103.00	$103.00	$103.00
Purchase #4	$137.45	11.665%	$153.4835	$153.48	$153.50	$153.50
Purchase #5	$132.91	8.285%	$143.9216	$143.92	$143.90	$143.90
Purchase #6	$249.69	10.491%	$275.885	$275.89	$275.90	$275.90
Purchase #7	$179.92	3.264%	$185.7926	$185.79	$185.80	$185.80
7 purchase totals =	$886.84		$964.8941	$964.88	$964.90	$964.90