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	$30.78	12.516%	$34.6324	$34.63	$34.65	$34.60
Purchase #2	$218.68	12.798%	$246.6667	$246.67	$246.65	$246.70
Purchase #3	$37.65	11.118%	$41.8359	$41.84	$41.85	$41.80
Purchase #4	$86.57	3.733%	$89.8017	$89.80	$89.80	$89.80
Purchase #5	$56.57	5.478%	$59.6689	$59.67	$59.65	$59.70
Purchase #6	$227.79	8.811%	$247.8606	$247.86	$247.85	$247.90
Purchase #7	$38.43	9.447%	$42.0605	$42.06	$42.05	$42.10
7 purchase totals =	$696.47		$762.5267	$762.53	$762.50	$762.60