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	$63.40	4.122%	$66.0133	$66.01	$66.00	$66.00
Purchase #2	$159.63	3.732%	$165.5874	$165.59	$165.60	$165.60
Purchase #3	$47.39	10.270%	$52.257	$52.26	$52.25	$52.30
Purchase #4	$26.33	4.863%	$27.6104	$27.61	$27.60	$27.60
Purchase #5	$148.65	3.859%	$154.3864	$154.39	$154.40	$154.40
Purchase #6	$22.70	10.445%	$25.071	$25.07	$25.05	$25.10
Purchase #7	$82.54	12.115%	$92.5397	$92.54	$92.55	$92.50
7 purchase totals =	$550.64		$583.4652	$583.47	$583.45	$583.50