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	$6.59	6.168%	$6.9965	$7.00	$7.00	$7.00
Purchase #2	$92.32	12.273%	$103.6504	$103.65	$103.65	$103.70
Purchase #3	$98.83	9.843%	$108.5578	$108.56	$108.55	$108.60
Purchase #4	$117.54	12.705%	$132.4735	$132.47	$132.45	$132.50
Purchase #5	$126.63	13.407%	$143.6073	$143.61	$143.60	$143.60
Purchase #6	$163.73	4.508%	$171.1109	$171.11	$171.10	$171.10
Purchase #7	$13.68	9.112%	$14.9265	$14.93	$14.95	$14.90
7 purchase totals =	$619.32		$681.3229	$681.33	$681.30	$681.40