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	$35.95	7.681%	$38.7113	$38.71	$38.70	$38.70
Purchase #2	$158.89	4.808%	$166.5294	$166.53	$166.55	$166.50
Purchase #3	$93.95	9.572%	$102.9429	$102.94	$102.95	$102.90
Purchase #4	$12.61	9.328%	$13.7863	$13.79	$13.80	$13.80
Purchase #5	$140.93	5.243%	$148.319	$148.32	$148.30	$148.30
Purchase #6	$132.42	6.769%	$141.3835	$141.38	$141.40	$141.40
Purchase #7	$90.66	9.860%	$99.5991	$99.60	$99.60	$99.60
7 purchase totals =	$665.41		$711.2715	$711.27	$711.30	$711.20