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	$205.79	11.742%	$229.9539	$229.95	$229.95	$230.00
Purchase #2	$189.83	4.619%	$198.5982	$198.60	$198.60	$198.60
Purchase #3	$102.69	12.801%	$115.8353	$115.84	$115.85	$115.80
Purchase #4	$78.45	6.842%	$83.8175	$83.82	$83.80	$83.80
Purchase #5	$98.50	5.773%	$104.1864	$104.19	$104.20	$104.20
Purchase #6	$175.93	8.186%	$190.3316	$190.33	$190.35	$190.30
Purchase #7	$162.71	9.323%	$177.8795	$177.88	$177.90	$177.90
7 purchase totals =	$1,013.90		$1,100.6024	$1,100.61	$1,100.65	$1,100.60