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	$12.64	8.804%	$13.7528	$13.75	$13.75	$13.80
Purchase #2	$93.46	12.657%	$105.2892	$105.29	$105.30	$105.30
Purchase #3	$203.63	5.697%	$215.2308	$215.23	$215.25	$215.20
Purchase #4	$39.55	5.400%	$41.6857	$41.69	$41.70	$41.70
Purchase #5	$38.34	5.602%	$40.4878	$40.49	$40.50	$40.50
Purchase #6	$78.68	9.307%	$86.0027	$86.00	$86.00	$86.00
Purchase #7	$159.67	3.409%	$165.1132	$165.11	$165.10	$165.10
7 purchase totals =	$625.97		$667.5622	$667.56	$667.60	$667.60