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	$153.39	5.186%	$161.3448	$161.34	$161.35	$161.30
Purchase #2	$69.25	12.365%	$77.8128	$77.81	$77.80	$77.80
Purchase #3	$105.92	7.283%	$113.6342	$113.63	$113.65	$113.60
Purchase #4	$128.45	12.378%	$144.3495	$144.35	$144.35	$144.30
Purchase #5	$249.87	12.256%	$280.4941	$280.49	$280.50	$280.50
Purchase #6	$222.95	4.570%	$233.1388	$233.14	$233.15	$233.10
Purchase #7	$49.38	12.233%	$55.4207	$55.42	$55.40	$55.40
7 purchase totals =	$979.21		$1,066.1949	$1,066.18	$1,066.20	$1,066.00