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	$229.59	13.219%	$259.9395	$259.94	$259.95	$259.90
Purchase #2	$44.31	5.305%	$46.6606	$46.66	$46.65	$46.70
Purchase #3	$142.91	8.405%	$154.9216	$154.92	$154.90	$154.90
Purchase #4	$71.64	6.321%	$76.1684	$76.17	$76.15	$76.20
Purchase #5	$162.78	7.202%	$174.5034	$174.50	$174.50	$174.50
Purchase #6	$93.49	7.274%	$100.2905	$100.29	$100.30	$100.30
Purchase #7	$59.71	12.271%	$67.037	$67.04	$67.05	$67.00
7 purchase totals =	$804.43		$879.5210	$879.52	$879.50	$879.50