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	$159.65	8.292%	$172.8882	$172.89	$172.90	$172.90
Purchase #2	$200.91	9.219%	$219.4319	$219.43	$219.45	$219.40
Purchase #3	$88.77	7.189%	$95.1517	$95.15	$95.15	$95.20
Purchase #4	$57.67	13.863%	$65.6648	$65.66	$65.65	$65.70
Purchase #5	$85.94	12.299%	$96.5098	$96.51	$96.50	$96.50
Purchase #6	$177.79	11.314%	$197.9052	$197.91	$197.90	$197.90
Purchase #7	$198.73	10.163%	$218.9269	$218.93	$218.95	$218.90
7 purchase totals =	$969.46		$1,066.4785	$1,066.48	$1,066.50	$1,066.50