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	$34.73	11.209%	$38.6229	$38.62	$38.60	$38.60
Purchase #2	$114.48	8.182%	$123.8468	$123.85	$123.85	$123.80
Purchase #3	$84.31	12.552%	$94.8926	$94.89	$94.90	$94.90
Purchase #4	$81.39	12.370%	$91.4579	$91.46	$91.45	$91.50
Purchase #5	$81.73	7.228%	$87.6374	$87.64	$87.65	$87.60
Purchase #6	$6.46	3.266%	$6.671	$6.67	$6.65	$6.70
Purchase #7	$153.72	12.338%	$172.686	$172.69	$172.70	$172.70
7 purchase totals =	$556.82		$615.8146	$615.82	$615.80	$615.80