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	$188.56	12.513%	$212.1545	$212.15	$212.15	$212.20
Purchase #2	$177.55	10.476%	$196.1501	$196.15	$196.15	$196.20
Purchase #3	$13.50	4.179%	$14.0642	$14.06	$14.05	$14.10
Purchase #4	$138.42	12.577%	$155.8291	$155.83	$155.85	$155.80
Purchase #5	$78.33	7.660%	$84.3301	$84.33	$84.35	$84.30
Purchase #6	$229.87	6.692%	$245.2529	$245.25	$245.25	$245.30
Purchase #7	$77.68	5.575%	$82.0107	$82.01	$82.00	$82.00
7 purchase totals =	$903.91		$989.7916	$989.78	$989.80	$989.90