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	$35.49	10.722%	$39.2952	$39.30	$39.30	$39.30
Purchase #2	$14.41	3.307%	$14.8865	$14.89	$14.90	$14.90
Purchase #3	$41.67	13.426%	$47.2646	$47.26	$47.25	$47.30
Purchase #4	$155.86	7.784%	$167.9921	$167.99	$168.00	$168.00
Purchase #5	$243.46	13.164%	$275.5091	$275.51	$275.50	$275.50
Purchase #6	$9.48	9.354%	$10.3668	$10.37	$10.35	$10.40
Purchase #7	$105.72	4.126%	$110.082	$110.08	$110.10	$110.10
7 purchase totals =	$606.09		$665.3963	$665.40	$665.40	$665.50