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	$13.43	12.111%	$15.0565	$15.06	$15.05	$15.10
Purchase #2	$88.34	13.159%	$99.9647	$99.96	$99.95	$100.00
Purchase #3	$107.32	3.847%	$111.4486	$111.45	$111.45	$111.40
Purchase #4	$201.42	10.426%	$222.42	$222.42	$222.40	$222.40
Purchase #5	$216.38	8.734%	$235.2786	$235.28	$235.30	$235.30
Purchase #6	$200.67	7.364%	$215.4473	$215.45	$215.45	$215.40
Purchase #7	$47.27	4.783%	$49.5309	$49.53	$49.55	$49.50
7 purchase totals =	$874.83		$949.1466	$949.15	$949.15	$949.10