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	$37.44	4.347%	$39.0675	$39.07	$39.05	$39.10
Purchase #2	$191.83	9.757%	$210.5469	$210.55	$210.55	$210.50
Purchase #3	$75.60	9.614%	$82.8682	$82.87	$82.85	$82.90
Purchase #4	$138.35	9.340%	$151.2719	$151.27	$151.25	$151.30
Purchase #5	$174.94	13.722%	$198.9453	$198.95	$198.95	$198.90
Purchase #6	$76.95	3.852%	$79.9141	$79.91	$79.90	$79.90
Purchase #7	$139.78	3.575%	$144.7771	$144.78	$144.80	$144.80
7 purchase totals =	$834.89		$907.3910	$907.40	$907.35	$907.40