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	$180.73	7.256%	$193.8438	$193.84	$193.85	$193.80
Purchase #2	$240.75	6.523%	$256.4541	$256.45	$256.45	$256.50
Purchase #3	$152.59	12.403%	$171.5157	$171.52	$171.50	$171.50
Purchase #4	$162.91	10.296%	$179.6832	$179.68	$179.70	$179.70
Purchase #5	$93.46	7.565%	$100.5302	$100.53	$100.55	$100.50
Purchase #6	$49.52	9.107%	$54.0298	$54.03	$54.05	$54.00
Purchase #7	$74.39	11.177%	$82.7046	$82.70	$82.70	$82.70
7 purchase totals =	$954.35		$1,038.7614	$1,038.75	$1,038.80	$1,038.70