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	$61.25	8.641%	$66.5426	$66.54	$66.55	$66.50
Purchase #2	$185.81	7.290%	$199.3555	$199.36	$199.35	$199.40
Purchase #3	$12.90	8.130%	$13.9488	$13.95	$13.95	$13.90
Purchase #4	$167.29	7.204%	$179.3416	$179.34	$179.35	$179.30
Purchase #5	$35.79	12.705%	$40.3371	$40.34	$40.35	$40.30
Purchase #6	$36.97	11.131%	$41.0851	$41.09	$41.10	$41.10
Purchase #7	$74.26	5.429%	$78.2916	$78.29	$78.30	$78.30
7 purchase totals =	$574.27		$618.9023	$618.91	$618.95	$618.80