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	$123.89	3.320%	$128.0031	$128.00	$128.00	$128.00
Purchase #2	$131.33	6.365%	$139.6892	$139.69	$139.70	$139.70
Purchase #3	$61.54	7.300%	$66.0324	$66.03	$66.05	$66.00
Purchase #4	$72.53	6.512%	$77.2532	$77.25	$77.25	$77.30
Purchase #5	$229.89	5.183%	$241.8052	$241.81	$241.80	$241.80
Purchase #6	$14.31	7.712%	$15.4136	$15.41	$15.40	$15.40
Purchase #7	$66.94	13.728%	$76.1295	$76.13	$76.15	$76.10
7 purchase totals =	$700.43		$744.3262	$744.32	$744.35	$744.30