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	$39.77	9.712%	$43.6325	$43.63	$43.65	$43.60
Purchase #2	$136.41	4.742%	$142.8786	$142.88	$142.90	$142.90
Purchase #3	$46.49	6.647%	$49.5802	$49.58	$49.60	$49.60
Purchase #4	$163.96	5.801%	$173.4713	$173.47	$173.45	$173.50
Purchase #5	$92.33	6.368%	$98.2096	$98.21	$98.20	$98.20
Purchase #6	$40.90	3.810%	$42.4583	$42.46	$42.45	$42.50
Purchase #7	$30.97	7.325%	$33.2386	$33.24	$33.25	$33.20
7 purchase totals =	$550.83		$583.4691	$583.47	$583.50	$583.50