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	$65.38	3.640%	$67.7598	$67.76	$67.75	$67.80
Purchase #2	$40.97	3.621%	$42.4535	$42.45	$42.45	$42.50
Purchase #3	$154.87	10.127%	$170.5537	$170.55	$170.55	$170.60
Purchase #4	$91.84	10.239%	$101.2435	$101.24	$101.25	$101.20
Purchase #5	$122.66	4.557%	$128.2496	$128.25	$128.25	$128.20
Purchase #6	$224.32	11.384%	$249.8566	$249.86	$249.85	$249.90
Purchase #7	$151.96	8.587%	$165.0088	$165.01	$165.00	$165.00
7 purchase totals =	$852.00		$925.1255	$925.12	$925.10	$925.20