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	$26.57	8.480%	$28.8231	$28.82	$28.80	$28.80
Purchase #2	$94.72	11.766%	$105.8648	$105.86	$105.85	$105.90
Purchase #3	$160.81	5.593%	$169.8041	$169.80	$169.80	$169.80
Purchase #4	$92.87	6.115%	$98.549	$98.55	$98.55	$98.50
Purchase #5	$65.48	7.448%	$70.357	$70.36	$70.35	$70.40
Purchase #6	$19.66	4.746%	$20.5931	$20.59	$20.60	$20.60
Purchase #7	$94.90	9.844%	$104.242	$104.24	$104.25	$104.20
7 purchase totals =	$555.01		$598.2331	$598.22	$598.20	$598.20