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	$99.29	6.665%	$105.9077	$105.91	$105.90	$105.90
Purchase #2	$73.74	9.806%	$80.9709	$80.97	$80.95	$81.00
Purchase #3	$100.29	13.233%	$113.5614	$113.56	$113.55	$113.60
Purchase #4	$92.58	3.425%	$95.7509	$95.75	$95.75	$95.80
Purchase #5	$60.37	3.305%	$62.3652	$62.37	$62.35	$62.40
Purchase #6	$150.32	9.709%	$164.9146	$164.91	$164.90	$164.90
Purchase #7	$103.79	12.715%	$116.9869	$116.99	$117.00	$117.00
7 purchase totals =	$680.38		$740.4576	$740.46	$740.40	$740.60