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	$53.55	10.218%	$59.0217	$59.02	$59.00	$59.00
Purchase #2	$107.68	3.700%	$111.6642	$111.66	$111.65	$111.70
Purchase #3	$126.86	9.760%	$139.2415	$139.24	$139.25	$139.20
Purchase #4	$60.40	9.711%	$66.2654	$66.27	$66.25	$66.30
Purchase #5	$58.37	12.582%	$65.7141	$65.71	$65.70	$65.70
Purchase #6	$249.97	11.680%	$279.1665	$279.17	$279.15	$279.20
Purchase #7	$24.55	6.440%	$26.131	$26.13	$26.15	$26.10
7 purchase totals =	$681.38		$747.2044	$747.20	$747.15	$747.20