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	$52.70	13.252%	$59.6838	$59.68	$59.70	$59.70
Purchase #2	$131.52	13.168%	$148.8386	$148.84	$148.85	$148.80
Purchase #3	$172.69	9.649%	$189.3529	$189.35	$189.35	$189.40
Purchase #4	$133.61	6.182%	$141.8698	$141.87	$141.85	$141.90
Purchase #5	$52.35	11.748%	$58.5001	$58.50	$58.50	$58.50
Purchase #6	$207.88	5.290%	$218.8769	$218.88	$218.90	$218.90
Purchase #7	$125.52	12.844%	$141.6418	$141.64	$141.65	$141.60
7 purchase totals =	$876.27		$958.7639	$958.76	$958.80	$958.80