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	$128.92	12.502%	$145.0376	$145.04	$145.05	$145.00
Purchase #2	$205.66	5.123%	$216.196	$216.20	$216.20	$216.20
Purchase #3	$82.37	8.257%	$89.1713	$89.17	$89.15	$89.20
Purchase #4	$28.54	10.450%	$31.5224	$31.52	$31.50	$31.50
Purchase #5	$27.62	12.493%	$31.0706	$31.07	$31.05	$31.10
Purchase #6	$102.85	13.393%	$116.6247	$116.62	$116.60	$116.60
Purchase #7	$72.49	10.454%	$80.0681	$80.07	$80.05	$80.10
7 purchase totals =	$648.45		$709.6907	$709.69	$709.60	$709.70