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	$106.80	10.868%	$118.407	$118.41	$118.40	$118.40
Purchase #2	$182.94	3.227%	$188.8435	$188.84	$188.85	$188.80
Purchase #3	$144.60	4.347%	$150.8858	$150.89	$150.90	$150.90
Purchase #4	$89.85	6.788%	$95.949	$95.95	$95.95	$95.90
Purchase #5	$134.52	11.517%	$150.0127	$150.01	$150.00	$150.00
Purchase #6	$154.65	5.378%	$162.9671	$162.97	$162.95	$163.00
Purchase #7	$82.44	10.345%	$90.9684	$90.97	$90.95	$91.00
7 purchase totals =	$895.80		$958.0335	$958.04	$958.00	$958.00