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	$94.38	6.623%	$100.6308	$100.63	$100.65	$100.60
Purchase #2	$127.37	10.697%	$140.9948	$140.99	$141.00	$141.00
Purchase #3	$34.46	12.661%	$38.823	$38.82	$38.80	$38.80
Purchase #4	$42.75	7.273%	$45.8592	$45.86	$45.85	$45.90
Purchase #5	$158.93	13.642%	$180.6112	$180.61	$180.60	$180.60
Purchase #6	$109.45	8.730%	$119.005	$119.01	$119.00	$119.00
Purchase #7	$195.90	11.242%	$217.9231	$217.92	$217.90	$217.90
7 purchase totals =	$763.24		$843.8471	$843.84	$843.80	$843.80