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	$18.66	12.245%	$20.9449	$20.94	$20.95	$20.90
Purchase #2	$86.86	6.812%	$92.7769	$92.78	$92.80	$92.80
Purchase #3	$136.63	3.584%	$141.5268	$141.53	$141.55	$141.50
Purchase #4	$129.72	11.667%	$144.8544	$144.85	$144.85	$144.90
Purchase #5	$151.71	5.763%	$160.453	$160.45	$160.45	$160.50
Purchase #6	$94.25	9.146%	$102.8701	$102.87	$102.85	$102.90
Purchase #7	$69.67	9.658%	$76.3987	$76.40	$76.40	$76.40
7 purchase totals =	$687.50		$739.8248	$739.82	$739.85	$739.90