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	$81.62	9.820%	$89.6351	$89.64	$89.65	$89.60
Purchase #2	$240.74	13.143%	$272.3805	$272.38	$272.40	$272.40
Purchase #3	$137.74	11.247%	$153.2316	$153.23	$153.25	$153.20
Purchase #4	$231.28	4.200%	$240.9938	$240.99	$241.00	$241.00
Purchase #5	$116.71	7.430%	$125.3816	$125.38	$125.40	$125.40
Purchase #6	$72.91	7.358%	$78.2747	$78.27	$78.25	$78.30
Purchase #7	$222.37	7.138%	$238.2428	$238.24	$238.25	$238.20
7 purchase totals =	$1,103.37		$1,198.1401	$1,198.13	$1,198.20	$1,198.10