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	$11.85	6.253%	$12.591	$12.59	$12.60	$12.60
Purchase #2	$219.77	11.235%	$244.4612	$244.46	$244.45	$244.50
Purchase #3	$90.56	9.561%	$99.2184	$99.22	$99.20	$99.20
Purchase #4	$104.42	5.237%	$109.8885	$109.89	$109.90	$109.90
Purchase #5	$61.97	10.549%	$68.5072	$68.51	$68.50	$68.50
Purchase #6	$29.85	3.798%	$30.9837	$30.98	$31.00	$31.00
Purchase #7	$93.95	5.141%	$98.78	$98.78	$98.80	$98.80
7 purchase totals =	$612.37		$664.4300	$664.43	$664.45	$664.50