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	$25.84	9.690%	$28.3439	$28.34	$28.35	$28.30
Purchase #2	$241.37	5.514%	$254.6791	$254.68	$254.70	$254.70
Purchase #3	$57.87	6.634%	$61.7091	$61.71	$61.70	$61.70
Purchase #4	$128.43	13.509%	$145.7796	$145.78	$145.80	$145.80
Purchase #5	$226.32	8.461%	$245.4689	$245.47	$245.45	$245.50
Purchase #6	$126.89	9.564%	$139.0258	$139.03	$139.05	$139.00
Purchase #7	$247.70	6.771%	$264.4718	$264.47	$264.45	$264.50
7 purchase totals =	$1,054.42		$1,139.4782	$1,139.48	$1,139.50	$1,139.50