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	$232.56	11.477%	$259.2509	$259.25	$259.25	$259.30
Purchase #2	$39.59	6.473%	$42.1527	$42.15	$42.15	$42.20
Purchase #3	$64.92	10.277%	$71.5918	$71.59	$71.60	$71.60
Purchase #4	$30.49	11.335%	$33.946	$33.95	$33.95	$33.90
Purchase #5	$10.69	12.379%	$12.0133	$12.01	$12.00	$12.00
Purchase #6	$184.65	13.765%	$210.0671	$210.07	$210.05	$210.10
Purchase #7	$205.81	7.545%	$221.3384	$221.34	$221.35	$221.30
7 purchase totals =	$768.71		$850.3602	$850.36	$850.35	$850.40