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	$138.83	4.724%	$145.3883	$145.39	$145.40	$145.40
Purchase #2	$143.58	3.414%	$148.4818	$148.48	$148.50	$148.50
Purchase #3	$112.69	6.417%	$119.9213	$119.92	$119.90	$119.90
Purchase #4	$142.43	9.730%	$156.2884	$156.29	$156.30	$156.30
Purchase #5	$144.86	7.383%	$155.555	$155.56	$155.55	$155.60
Purchase #6	$138.85	6.345%	$147.66	$147.66	$147.65	$147.70
Purchase #7	$21.60	11.610%	$24.1078	$24.11	$24.10	$24.10
7 purchase totals =	$842.84		$897.4026	$897.41	$897.40	$897.50