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	$9.55	8.320%	$10.3446	$10.34	$10.35	$10.30
Purchase #2	$60.81	9.718%	$66.7195	$66.72	$66.70	$66.70
Purchase #3	$196.48	12.710%	$221.4526	$221.45	$221.45	$221.50
Purchase #4	$5.53	7.264%	$5.9317	$5.93	$5.95	$5.90
Purchase #5	$126.83	4.264%	$132.238	$132.24	$132.25	$132.20
Purchase #6	$199.99	11.160%	$222.3089	$222.31	$222.30	$222.30
Purchase #7	$69.91	12.253%	$78.4761	$78.48	$78.50	$78.50
7 purchase totals =	$669.10		$737.4714	$737.47	$737.50	$737.40