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	$139.47	10.773%	$154.4951	$154.50	$154.50	$154.50
Purchase #2	$67.51	7.226%	$72.3883	$72.39	$72.40	$72.40
Purchase #3	$28.94	4.689%	$30.297	$30.30	$30.30	$30.30
Purchase #4	$164.28	5.178%	$172.7864	$172.79	$172.80	$172.80
Purchase #5	$138.82	11.453%	$154.7191	$154.72	$154.70	$154.70
Purchase #6	$29.90	8.638%	$32.4828	$32.48	$32.50	$32.50
Purchase #7	$78.71	4.274%	$82.0741	$82.07	$82.05	$82.10
7 purchase totals =	$647.63		$699.2428	$699.25	$699.25	$699.30