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	$77.87	3.167%	$80.3361	$80.34	$80.35	$80.30
Purchase #2	$170.71	10.870%	$189.2662	$189.27	$189.25	$189.30
Purchase #3	$158.75	4.632%	$166.1033	$166.10	$166.10	$166.10
Purchase #4	$171.47	3.160%	$176.8885	$176.89	$176.90	$176.90
Purchase #5	$216.68	3.154%	$223.5141	$223.51	$223.50	$223.50
Purchase #6	$193.44	13.120%	$218.8193	$218.82	$218.80	$218.80
Purchase #7	$107.97	3.243%	$111.4715	$111.47	$111.45	$111.50
7 purchase totals =	$1,096.89		$1,166.3990	$1,166.40	$1,166.35	$1,166.40