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	$131.80	6.669%	$140.5897	$140.59	$140.60	$140.60
Purchase #2	$146.37	8.241%	$158.4324	$158.43	$158.45	$158.40
Purchase #3	$103.90	9.588%	$113.8619	$113.86	$113.85	$113.90
Purchase #4	$141.84	10.555%	$156.8112	$156.81	$156.80	$156.80
Purchase #5	$217.26	7.741%	$234.0781	$234.08	$234.10	$234.10
Purchase #6	$123.65	11.617%	$138.0144	$138.01	$138.00	$138.00
Purchase #7	$79.51	12.121%	$89.1474	$89.15	$89.15	$89.10
7 purchase totals =	$944.33		$1,030.9351	$1,030.93	$1,030.95	$1,030.90