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	$170.95	5.484%	$180.3249	$180.32	$180.30	$180.30
Purchase #2	$153.55	12.315%	$172.4597	$172.46	$172.45	$172.50
Purchase #3	$148.83	10.572%	$164.5643	$164.56	$164.55	$164.60
Purchase #4	$72.75	6.508%	$77.4846	$77.48	$77.50	$77.50
Purchase #5	$84.46	3.778%	$87.6509	$87.65	$87.65	$87.70
Purchase #6	$66.75	12.194%	$74.8895	$74.89	$74.90	$74.90
Purchase #7	$70.32	8.751%	$76.4737	$76.47	$76.45	$76.50
7 purchase totals =	$767.61		$833.8476	$833.83	$833.80	$834.00