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	$138.72	9.279%	$151.5918	$151.59	$151.60	$151.60
Purchase #2	$146.73	11.670%	$163.8534	$163.85	$163.85	$163.90
Purchase #3	$144.59	6.425%	$153.8799	$153.88	$153.90	$153.90
Purchase #4	$109.35	10.153%	$120.4523	$120.45	$120.45	$120.50
Purchase #5	$48.56	8.855%	$52.86	$52.86	$52.85	$52.90
Purchase #6	$28.65	10.150%	$31.558	$31.56	$31.55	$31.60
Purchase #7	$141.83	13.258%	$160.6338	$160.63	$160.65	$160.60
7 purchase totals =	$758.43		$834.8292	$834.82	$834.85	$835.00