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	$126.37	3.712%	$131.0609	$131.06	$131.05	$131.10
Purchase #2	$49.90	5.246%	$52.5178	$52.52	$52.50	$52.50
Purchase #3	$94.49	11.136%	$105.0124	$105.01	$105.00	$105.00
Purchase #4	$89.32	13.864%	$101.7033	$101.70	$101.70	$101.70
Purchase #5	$216.92	7.110%	$232.343	$232.34	$232.35	$232.30
Purchase #6	$43.52	11.247%	$48.4147	$48.41	$48.40	$48.40
Purchase #7	$162.52	10.831%	$180.1225	$180.12	$180.10	$180.10
7 purchase totals =	$783.04		$851.1746	$851.16	$851.10	$851.10