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	$28.47	9.735%	$31.2416	$31.24	$31.25	$31.20
Purchase #2	$158.89	13.242%	$179.9302	$179.93	$179.95	$179.90
Purchase #3	$235.99	12.219%	$264.8256	$264.83	$264.85	$264.80
Purchase #4	$238.64	3.678%	$247.4172	$247.42	$247.40	$247.40
Purchase #5	$231.34	11.634%	$258.2541	$258.25	$258.25	$258.30
Purchase #6	$9.51	5.186%	$10.0032	$10.00	$10.00	$10.00
Purchase #7	$166.54	12.215%	$186.8829	$186.88	$186.90	$186.90
7 purchase totals =	$1,069.38		$1,178.5548	$1,178.55	$1,178.60	$1,178.50