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	$37.57	11.822%	$42.0115	$42.01	$42.00	$42.00
Purchase #2	$56.96	9.580%	$62.4168	$62.42	$62.40	$62.40
Purchase #3	$115.87	3.307%	$119.7018	$119.70	$119.70	$119.70
Purchase #4	$28.59	9.394%	$31.2757	$31.28	$31.30	$31.30
Purchase #5	$34.59	10.801%	$38.3261	$38.33	$38.35	$38.30
Purchase #6	$239.96	11.861%	$268.4217	$268.42	$268.40	$268.40
Purchase #7	$94.83	4.250%	$98.8603	$98.86	$98.85	$98.90
7 purchase totals =	$608.37		$661.0139	$661.02	$661.00	$661.00