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	$85.90	13.862%	$97.8075	$97.81	$97.80	$97.80
Purchase #2	$50.36	12.141%	$56.4742	$56.47	$56.45	$56.50
Purchase #3	$131.58	3.545%	$136.2445	$136.24	$136.25	$136.20
Purchase #4	$29.87	10.189%	$32.9135	$32.91	$32.90	$32.90
Purchase #5	$92.42	7.800%	$99.6288	$99.63	$99.65	$99.60
Purchase #6	$135.93	7.416%	$146.0106	$146.01	$146.00	$146.00
Purchase #7	$111.84	10.253%	$123.307	$123.31	$123.30	$123.30
7 purchase totals =	$637.90		$692.3861	$692.38	$692.35	$692.30