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	$136.97	4.279%	$142.8309	$142.83	$142.85	$142.80
Purchase #2	$150.54	7.724%	$162.1677	$162.17	$162.15	$162.20
Purchase #3	$46.27	6.104%	$49.0943	$49.09	$49.10	$49.10
Purchase #4	$104.99	12.169%	$117.7662	$117.77	$117.75	$117.80
Purchase #5	$9.42	11.550%	$10.508	$10.51	$10.50	$10.50
Purchase #6	$104.98	3.814%	$108.9839	$108.98	$109.00	$109.00
Purchase #7	$170.46	6.460%	$181.4717	$181.47	$181.45	$181.50
7 purchase totals =	$723.63		$772.8227	$772.82	$772.80	$772.90