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	$36.94	6.671%	$39.4043	$39.40	$39.40	$39.40
Purchase #2	$97.35	7.479%	$104.6308	$104.63	$104.65	$104.60
Purchase #3	$59.29	13.146%	$67.0843	$67.08	$67.10	$67.10
Purchase #4	$250.48	8.793%	$272.5047	$272.50	$272.50	$272.50
Purchase #5	$6.37	3.634%	$6.6015	$6.60	$6.60	$6.60
Purchase #6	$212.83	12.270%	$238.9442	$238.94	$238.95	$238.90
Purchase #7	$250.47	10.221%	$276.0705	$276.07	$276.05	$276.10
7 purchase totals =	$913.73		$1,005.2403	$1,005.22	$1,005.25	$1,005.20