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	$75.75	5.823%	$80.1609	$80.16	$80.15	$80.20
Purchase #2	$74.55	5.366%	$78.5504	$78.55	$78.55	$78.60
Purchase #3	$167.43	3.715%	$173.65	$173.65	$173.65	$173.70
Purchase #4	$131.86	8.455%	$143.0088	$143.01	$143.00	$143.00
Purchase #5	$137.51	11.134%	$152.8204	$152.82	$152.80	$152.80
Purchase #6	$40.71	4.756%	$42.6462	$42.65	$42.65	$42.60
Purchase #7	$92.34	4.690%	$96.6707	$96.67	$96.65	$96.70
7 purchase totals =	$720.15		$767.5074	$767.51	$767.45	$767.60