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	$36.73	3.398%	$37.9781	$37.98	$38.00	$38.00
Purchase #2	$95.35	5.769%	$100.8507	$100.85	$100.85	$100.90
Purchase #3	$150.86	9.726%	$165.5326	$165.53	$165.55	$165.50
Purchase #4	$21.67	10.628%	$23.9731	$23.97	$23.95	$24.00
Purchase #5	$19.30	8.484%	$20.9374	$20.94	$20.95	$20.90
Purchase #6	$246.68	10.210%	$271.866	$271.87	$271.85	$271.90
Purchase #7	$179.76	9.557%	$196.9397	$196.94	$196.95	$196.90
7 purchase totals =	$750.35		$818.0776	$818.08	$818.10	$818.10