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	$103.68	3.140%	$106.9356	$106.94	$106.95	$106.90
Purchase #2	$146.60	13.800%	$166.8308	$166.83	$166.85	$166.80
Purchase #3	$73.89	12.204%	$82.9075	$82.91	$82.90	$82.90
Purchase #4	$43.65	8.832%	$47.5052	$47.51	$47.50	$47.50
Purchase #5	$75.37	10.450%	$83.2462	$83.25	$83.25	$83.20
Purchase #6	$87.91	8.516%	$95.3964	$95.40	$95.40	$95.40
Purchase #7	$76.94	10.772%	$85.228	$85.23	$85.25	$85.20
7 purchase totals =	$608.04		$668.0497	$668.07	$668.10	$667.90