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	$39.85	6.553%	$42.4614	$42.46	$42.45	$42.50
Purchase #2	$119.62	11.583%	$133.4756	$133.48	$133.50	$133.50
Purchase #3	$154.64	5.329%	$162.8808	$162.88	$162.90	$162.90
Purchase #4	$122.38	13.811%	$139.2819	$139.28	$139.30	$139.30
Purchase #5	$70.84	8.545%	$76.8933	$76.89	$76.90	$76.90
Purchase #6	$72.92	6.739%	$77.8341	$77.83	$77.85	$77.80
Purchase #7	$203.92	5.171%	$214.4647	$214.46	$214.45	$214.50
7 purchase totals =	$784.17		$847.2918	$847.28	$847.35	$847.40