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	$155.48	12.421%	$174.7922	$174.79	$174.80	$174.80
Purchase #2	$19.56	3.236%	$20.193	$20.19	$20.20	$20.20
Purchase #3	$154.32	11.464%	$172.0112	$172.01	$172.00	$172.00
Purchase #4	$152.39	10.604%	$168.5494	$168.55	$168.55	$168.50
Purchase #5	$204.71	10.242%	$225.6764	$225.68	$225.70	$225.70
Purchase #6	$96.37	3.307%	$99.557	$99.56	$99.55	$99.60
Purchase #7	$63.60	4.423%	$66.413	$66.41	$66.40	$66.40
7 purchase totals =	$846.43		$927.1922	$927.19	$927.20	$927.20