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	$130.37	11.531%	$145.403	$145.40	$145.40	$145.40
Purchase #2	$120.65	5.456%	$127.2327	$127.23	$127.25	$127.20
Purchase #3	$189.31	3.812%	$196.5265	$196.53	$196.55	$196.50
Purchase #4	$168.89	8.104%	$182.5768	$182.58	$182.60	$182.60
Purchase #5	$34.43	9.442%	$37.6809	$37.68	$37.70	$37.70
Purchase #6	$36.30	4.661%	$37.9919	$37.99	$38.00	$38.00
Purchase #7	$180.36	13.346%	$204.4308	$204.43	$204.45	$204.40
7 purchase totals =	$860.31		$931.8426	$931.84	$931.95	$931.80