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	$18.25	12.769%	$20.5803	$20.58	$20.60	$20.60
Purchase #2	$237.62	13.214%	$269.0191	$269.02	$269.00	$269.00
Purchase #3	$49.59	8.280%	$53.6961	$53.70	$53.70	$53.70
Purchase #4	$148.81	11.291%	$165.6121	$165.61	$165.60	$165.60
Purchase #5	$101.60	3.453%	$105.1082	$105.11	$105.10	$105.10
Purchase #6	$162.29	3.194%	$167.4735	$167.47	$167.45	$167.50
Purchase #7	$109.83	12.763%	$123.8476	$123.85	$123.85	$123.80
7 purchase totals =	$827.99		$905.3369	$905.34	$905.30	$905.30