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	$109.27	13.863%	$124.4181	$124.42	$124.40	$124.40
Purchase #2	$30.46	7.700%	$32.8054	$32.81	$32.80	$32.80
Purchase #3	$128.81	4.721%	$134.8911	$134.89	$134.90	$134.90
Purchase #4	$153.45	12.642%	$172.8491	$172.85	$172.85	$172.80
Purchase #5	$64.83	13.108%	$73.3279	$73.33	$73.35	$73.30
Purchase #6	$138.36	4.703%	$144.8671	$144.87	$144.85	$144.90
Purchase #7	$238.35	8.577%	$258.7933	$258.79	$258.80	$258.80
7 purchase totals =	$863.53		$941.9520	$941.96	$941.95	$941.90