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	$82.53	8.395%	$89.4584	$89.46	$89.45	$89.50
Purchase #2	$138.38	7.555%	$148.8346	$148.83	$148.85	$148.80
Purchase #3	$160.68	11.390%	$178.9815	$178.98	$179.00	$179.00
Purchase #4	$247.50	6.843%	$264.4364	$264.44	$264.45	$264.40
Purchase #5	$34.79	5.586%	$36.7334	$36.73	$36.75	$36.70
Purchase #6	$163.42	13.511%	$185.4997	$185.50	$185.50	$185.50
Purchase #7	$173.60	3.435%	$179.5632	$179.56	$179.55	$179.60
7 purchase totals =	$1,000.90		$1,083.5072	$1,083.50	$1,083.55	$1,083.50