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	$56.39	5.290%	$59.373	$59.37	$59.35	$59.40
Purchase #2	$228.90	10.431%	$252.7766	$252.78	$252.80	$252.80
Purchase #3	$29.73	11.478%	$33.1424	$33.14	$33.15	$33.10
Purchase #4	$70.93	3.255%	$73.2388	$73.24	$73.25	$73.20
Purchase #5	$171.83	9.247%	$187.7191	$187.72	$187.70	$187.70
Purchase #6	$52.86	9.568%	$57.9176	$57.92	$57.90	$57.90
Purchase #7	$10.38	7.310%	$11.1388	$11.14	$11.15	$11.10
7 purchase totals =	$621.02		$675.3063	$675.31	$675.30	$675.20