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	$235.82	8.609%	$256.1217	$256.12	$256.10	$256.10
Purchase #2	$90.38	12.143%	$101.3548	$101.35	$101.35	$101.40
Purchase #3	$94.72	10.812%	$104.9611	$104.96	$104.95	$105.00
Purchase #4	$77.96	10.341%	$86.0218	$86.02	$86.00	$86.00
Purchase #5	$17.67	12.499%	$19.8786	$19.88	$19.90	$19.90
Purchase #6	$93.81	10.523%	$103.6816	$103.68	$103.70	$103.70
Purchase #7	$154.91	6.182%	$164.4865	$164.49	$164.50	$164.50
7 purchase totals =	$765.27		$836.5061	$836.50	$836.50	$836.60