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	$52.93	5.314%	$55.7427	$55.74	$55.75	$55.70
Purchase #2	$37.83	4.213%	$39.4238	$39.42	$39.40	$39.40
Purchase #3	$227.71	12.294%	$255.7047	$255.70	$255.70	$255.70
Purchase #4	$59.38	10.649%	$65.7034	$65.70	$65.70	$65.70
Purchase #5	$67.76	7.254%	$72.6753	$72.68	$72.70	$72.70
Purchase #6	$229.87	7.212%	$246.4482	$246.45	$246.45	$246.40
Purchase #7	$110.56	7.154%	$118.4695	$118.47	$118.45	$118.50
7 purchase totals =	$786.04		$854.1676	$854.16	$854.15	$854.10