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	$135.26	6.714%	$144.3414	$144.34	$144.35	$144.30
Purchase #2	$246.70	8.348%	$267.2945	$267.29	$267.30	$267.30
Purchase #3	$11.41	3.272%	$11.7833	$11.78	$11.80	$11.80
Purchase #4	$129.72	11.320%	$144.4043	$144.40	$144.40	$144.40
Purchase #5	$11.41	9.591%	$12.5043	$12.50	$12.50	$12.50
Purchase #6	$240.29	6.385%	$255.6325	$255.63	$255.65	$255.60
Purchase #7	$81.92	10.623%	$90.6224	$90.62	$90.60	$90.60
7 purchase totals =	$856.71		$926.5827	$926.56	$926.60	$926.50