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	$88.75	12.178%	$99.558	$99.56	$99.55	$99.60
Purchase #2	$9.82	6.314%	$10.44	$10.44	$10.45	$10.40
Purchase #3	$29.89	8.328%	$32.3792	$32.38	$32.40	$32.40
Purchase #4	$124.28	12.535%	$139.8585	$139.86	$139.85	$139.90
Purchase #5	$249.42	4.627%	$260.9607	$260.96	$260.95	$261.00
Purchase #6	$134.82	3.195%	$139.1275	$139.13	$139.15	$139.10
Purchase #7	$87.48	11.855%	$97.8508	$97.85	$97.85	$97.90
7 purchase totals =	$724.46		$780.1747	$780.18	$780.20	$780.30