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	$108.42	4.538%	$113.3401	$113.34	$113.35	$113.30
Purchase #2	$109.94	7.353%	$118.0239	$118.02	$118.00	$118.00
Purchase #3	$163.89	9.428%	$179.3415	$179.34	$179.35	$179.30
Purchase #4	$47.70	6.104%	$50.6116	$50.61	$50.60	$50.60
Purchase #5	$89.83	7.137%	$96.2412	$96.24	$96.25	$96.20
Purchase #6	$81.38	10.552%	$89.9672	$89.97	$89.95	$90.00
Purchase #7	$19.91	6.387%	$21.1817	$21.18	$21.20	$21.20
7 purchase totals =	$621.07		$668.7072	$668.70	$668.70	$668.60