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	$81.77	11.787%	$91.4082	$91.41	$91.40	$91.40
Purchase #2	$104.81	7.833%	$113.0198	$113.02	$113.00	$113.00
Purchase #3	$200.33	4.255%	$208.854	$208.85	$208.85	$208.90
Purchase #4	$52.87	7.622%	$56.8998	$56.90	$56.90	$56.90
Purchase #5	$85.64	13.835%	$97.4883	$97.49	$97.50	$97.50
Purchase #6	$84.98	5.817%	$89.9233	$89.92	$89.90	$89.90
Purchase #7	$11.64	12.137%	$13.0527	$13.05	$13.05	$13.10
7 purchase totals =	$622.04		$670.6461	$670.64	$670.60	$670.70