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	$237.86	7.799%	$256.4107	$256.41	$256.40	$256.40
Purchase #2	$61.99	7.697%	$66.7614	$66.76	$66.75	$66.80
Purchase #3	$172.45	6.602%	$183.8351	$183.84	$183.85	$183.80
Purchase #4	$84.95	13.730%	$96.6136	$96.61	$96.60	$96.60
Purchase #5	$39.93	5.264%	$42.0319	$42.03	$42.05	$42.00
Purchase #6	$138.69	8.184%	$150.0404	$150.04	$150.05	$150.00
Purchase #7	$190.51	5.388%	$200.7747	$200.77	$200.75	$200.80
7 purchase totals =	$926.38		$996.4678	$996.46	$996.45	$996.40