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	$102.43	5.663%	$108.2306	$108.23	$108.25	$108.20
Purchase #2	$88.96	9.243%	$97.1826	$97.18	$97.20	$97.20
Purchase #3	$150.78	11.339%	$167.8769	$167.88	$167.90	$167.90
Purchase #4	$80.76	11.452%	$90.0086	$90.01	$90.00	$90.00
Purchase #5	$241.75	13.241%	$273.7601	$273.76	$273.75	$273.80
Purchase #6	$61.46	12.822%	$69.3404	$69.34	$69.35	$69.30
Purchase #7	$138.82	4.719%	$145.3709	$145.37	$145.35	$145.40
7 purchase totals =	$864.96		$951.7701	$951.77	$951.80	$951.80