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	$52.32	13.141%	$59.1954	$59.20	$59.20	$59.20
Purchase #2	$51.77	10.692%	$57.3052	$57.31	$57.30	$57.30
Purchase #3	$239.98	4.281%	$250.2535	$250.25	$250.25	$250.30
Purchase #4	$19.39	6.130%	$20.5786	$20.58	$20.60	$20.60
Purchase #5	$164.82	9.250%	$180.0659	$180.07	$180.05	$180.10
Purchase #6	$244.74	7.441%	$262.9511	$262.95	$262.95	$263.00
Purchase #7	$24.25	3.556%	$25.1123	$25.11	$25.10	$25.10
7 purchase totals =	$797.27		$855.4620	$855.47	$855.45	$855.60