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	$76.42	13.434%	$86.6863	$86.69	$86.70	$86.70
Purchase #2	$97.53	8.532%	$105.8513	$105.85	$105.85	$105.90
Purchase #3	$109.51	13.661%	$124.4702	$124.47	$124.45	$124.50
Purchase #4	$87.44	6.158%	$92.8246	$92.82	$92.80	$92.80
Purchase #5	$242.25	4.538%	$253.2433	$253.24	$253.25	$253.20
Purchase #6	$209.40	10.722%	$231.8519	$231.85	$231.85	$231.90
Purchase #7	$129.30	11.202%	$143.7842	$143.78	$143.80	$143.80
7 purchase totals =	$951.85		$1,038.7118	$1,038.70	$1,038.70	$1,038.80