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	$17.65	10.312%	$19.4701	$19.47	$19.45	$19.50
Purchase #2	$197.47	10.434%	$218.074	$218.07	$218.05	$218.10
Purchase #3	$160.27	5.744%	$169.4759	$169.48	$169.50	$169.50
Purchase #4	$157.76	8.605%	$171.3352	$171.34	$171.35	$171.30
Purchase #5	$70.54	13.788%	$80.2661	$80.27	$80.25	$80.30
Purchase #6	$104.77	6.237%	$111.3045	$111.30	$111.30	$111.30
Purchase #7	$47.69	10.143%	$52.5272	$52.53	$52.55	$52.50
7 purchase totals =	$756.15		$822.4530	$822.46	$822.45	$822.50