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	$242.56	12.417%	$272.6787	$272.68	$272.70	$272.70
Purchase #2	$57.92	6.114%	$61.4612	$61.46	$61.45	$61.50
Purchase #3	$59.72	9.678%	$65.4997	$65.50	$65.50	$65.50
Purchase #4	$151.82	4.432%	$158.5487	$158.55	$158.55	$158.50
Purchase #5	$129.31	10.672%	$143.11	$143.11	$143.10	$143.10
Purchase #6	$160.98	4.870%	$168.8197	$168.82	$168.80	$168.80
Purchase #7	$106.47	13.375%	$120.7104	$120.71	$120.70	$120.70
7 purchase totals =	$908.78		$990.8284	$990.83	$990.80	$990.80