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	$11.88	13.329%	$13.4635	$13.46	$13.45	$13.50
Purchase #2	$29.58	8.203%	$32.0064	$32.01	$32.00	$32.00
Purchase #3	$58.39	3.746%	$60.5773	$60.58	$60.60	$60.60
Purchase #4	$131.90	5.627%	$139.322	$139.32	$139.30	$139.30
Purchase #5	$83.79	6.146%	$88.9397	$88.94	$88.95	$88.90
Purchase #6	$91.81	3.624%	$95.1372	$95.14	$95.15	$95.10
Purchase #7	$190.48	10.304%	$210.1071	$210.11	$210.10	$210.10
7 purchase totals =	$597.83		$639.5532	$639.56	$639.55	$639.50