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	$102.34	9.106%	$111.6591	$111.66	$111.65	$111.70
Purchase #2	$123.55	10.265%	$136.2324	$136.23	$136.25	$136.20
Purchase #3	$111.30	11.173%	$123.7355	$123.74	$123.75	$123.70
Purchase #4	$52.30	3.658%	$54.2131	$54.21	$54.20	$54.20
Purchase #5	$168.65	6.488%	$179.592	$179.59	$179.60	$179.60
Purchase #6	$141.71	8.269%	$153.428	$153.43	$153.45	$153.40
Purchase #7	$250.83	8.342%	$271.7542	$271.75	$271.75	$271.80
7 purchase totals =	$950.68		$1,030.6143	$1,030.61	$1,030.65	$1,030.60