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	$67.84	6.861%	$72.4945	$72.49	$72.50	$72.50
Purchase #2	$134.99	6.123%	$143.2554	$143.26	$143.25	$143.30
Purchase #3	$220.33	6.470%	$234.5854	$234.59	$234.60	$234.60
Purchase #4	$50.57	10.522%	$55.891	$55.89	$55.90	$55.90
Purchase #5	$147.34	7.138%	$157.8571	$157.86	$157.85	$157.90
Purchase #6	$106.37	4.512%	$111.1694	$111.17	$111.15	$111.20
Purchase #7	$166.55	13.854%	$189.6238	$189.62	$189.60	$189.60
7 purchase totals =	$893.99		$964.8766	$964.88	$964.85	$965.00