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	$192.30	11.806%	$215.0029	$215.00	$215.00	$215.00
Purchase #2	$39.85	7.478%	$42.83	$42.83	$42.85	$42.80
Purchase #3	$138.66	3.417%	$143.398	$143.40	$143.40	$143.40
Purchase #4	$49.29	9.548%	$53.9962	$54.00	$54.00	$54.00
Purchase #5	$40.60	8.687%	$44.1269	$44.13	$44.15	$44.10
Purchase #6	$25.29	12.478%	$28.4457	$28.45	$28.45	$28.40
Purchase #7	$30.33	5.508%	$32.0006	$32.00	$32.00	$32.00
7 purchase totals =	$516.32		$559.8003	$559.81	$559.85	$559.70