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	$242.86	5.142%	$255.3479	$255.35	$255.35	$255.30
Purchase #2	$124.71	5.453%	$131.5104	$131.51	$131.50	$131.50
Purchase #3	$56.45	9.499%	$61.8122	$61.81	$61.80	$61.80
Purchase #4	$139.28	6.166%	$147.868	$147.87	$147.85	$147.90
Purchase #5	$13.89	4.618%	$14.5314	$14.53	$14.55	$14.50
Purchase #6	$66.88	8.813%	$72.7741	$72.77	$72.75	$72.80
Purchase #7	$39.91	13.258%	$45.2013	$45.20	$45.20	$45.20
7 purchase totals =	$683.98		$729.0453	$729.04	$729.00	$729.00