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	$90.49	9.871%	$99.4223	$99.42	$99.40	$99.40
Purchase #2	$229.61	8.611%	$249.3817	$249.38	$249.40	$249.40
Purchase #3	$98.83	3.596%	$102.3839	$102.38	$102.40	$102.40
Purchase #4	$95.93	3.119%	$98.9221	$98.92	$98.90	$98.90
Purchase #5	$20.56	3.240%	$21.2261	$21.23	$21.25	$21.20
Purchase #6	$156.27	10.170%	$172.1627	$172.16	$172.15	$172.20
Purchase #7	$17.63	10.697%	$19.5159	$19.52	$19.50	$19.50
7 purchase totals =	$709.32		$763.0147	$763.01	$763.00	$763.00