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	$54.36	9.109%	$59.3117	$59.31	$59.30	$59.30
Purchase #2	$107.98	10.208%	$119.0026	$119.00	$119.00	$119.00
Purchase #3	$214.36	12.864%	$241.9353	$241.94	$241.95	$241.90
Purchase #4	$169.86	7.843%	$183.1821	$183.18	$183.20	$183.20
Purchase #5	$64.57	12.783%	$72.824	$72.82	$72.80	$72.80
Purchase #6	$142.60	7.157%	$152.8059	$152.81	$152.80	$152.80
Purchase #7	$55.77	9.115%	$60.8534	$60.85	$60.85	$60.90
7 purchase totals =	$809.50		$889.9150	$889.91	$889.90	$889.90