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	$103.47	4.842%	$108.48	$108.48	$108.50	$108.50
Purchase #2	$27.79	3.670%	$28.8099	$28.81	$28.80	$28.80
Purchase #3	$27.90	3.288%	$28.8174	$28.82	$28.80	$28.80
Purchase #4	$127.79	13.752%	$145.3637	$145.36	$145.35	$145.40
Purchase #5	$163.85	10.301%	$180.7282	$180.73	$180.75	$180.70
Purchase #6	$225.96	5.364%	$238.0805	$238.08	$238.10	$238.10
Purchase #7	$224.67	11.550%	$250.6194	$250.62	$250.60	$250.60
7 purchase totals =	$901.43		$980.8991	$980.90	$980.90	$980.90