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	$54.49	8.268%	$58.9952	$59.00	$59.00	$59.00
Purchase #2	$43.48	5.355%	$45.8084	$45.81	$45.80	$45.80
Purchase #3	$221.36	9.253%	$241.8424	$241.84	$241.85	$241.80
Purchase #4	$160.43	11.741%	$179.2661	$179.27	$179.25	$179.30
Purchase #5	$108.71	10.863%	$120.5192	$120.52	$120.50	$120.50
Purchase #6	$77.93	5.524%	$82.2349	$82.23	$82.25	$82.20
Purchase #7	$172.84	3.313%	$178.5662	$178.57	$178.55	$178.60
7 purchase totals =	$839.24		$907.2324	$907.24	$907.20	$907.20