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	$52.93	13.375%	$60.0094	$60.01	$60.00	$60.00
Purchase #2	$88.39	9.506%	$96.7924	$96.79	$96.80	$96.80
Purchase #3	$132.75	8.375%	$143.8678	$143.87	$143.85	$143.90
Purchase #4	$39.47	13.596%	$44.8363	$44.84	$44.85	$44.80
Purchase #5	$72.92	7.221%	$78.1856	$78.19	$78.20	$78.20
Purchase #6	$132.85	8.675%	$144.3747	$144.37	$144.35	$144.40
Purchase #7	$109.27	9.256%	$119.384	$119.38	$119.40	$119.40
7 purchase totals =	$628.58		$687.4502	$687.45	$687.45	$687.50