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	$78.54	8.493%	$85.2104	$85.21	$85.20	$85.20
Purchase #2	$21.40	12.148%	$23.9997	$24.00	$24.00	$24.00
Purchase #3	$78.65	8.815%	$85.583	$85.58	$85.60	$85.60
Purchase #4	$46.99	13.149%	$53.1687	$53.17	$53.15	$53.20
Purchase #5	$230.33	11.264%	$256.2744	$256.27	$256.25	$256.30
Purchase #6	$174.74	3.287%	$180.4837	$180.48	$180.50	$180.50
Purchase #7	$146.60	13.460%	$166.3324	$166.33	$166.35	$166.30
7 purchase totals =	$777.25		$851.0523	$851.04	$851.05	$851.10