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	$106.99	7.225%	$114.72	$114.72	$114.70	$114.70
Purchase #2	$49.78	3.680%	$51.6119	$51.61	$51.60	$51.60
Purchase #3	$80.91	11.271%	$90.0294	$90.03	$90.05	$90.00
Purchase #4	$245.71	13.110%	$277.9226	$277.92	$277.90	$277.90
Purchase #5	$80.95	10.140%	$89.1583	$89.16	$89.15	$89.20
Purchase #6	$184.49	7.800%	$198.8802	$198.88	$198.90	$198.90
Purchase #7	$34.48	9.172%	$37.6425	$37.64	$37.65	$37.60
7 purchase totals =	$783.31		$859.9649	$859.96	$859.95	$859.90