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	$157.71	4.507%	$164.818	$164.82	$164.80	$164.80
Purchase #2	$133.29	9.221%	$145.5807	$145.58	$145.60	$145.60
Purchase #3	$161.53	11.122%	$179.4954	$179.50	$179.50	$179.50
Purchase #4	$75.30	13.240%	$85.2697	$85.27	$85.25	$85.30
Purchase #5	$224.64	11.567%	$250.6241	$250.62	$250.60	$250.60
Purchase #6	$221.43	4.521%	$231.4409	$231.44	$231.45	$231.40
Purchase #7	$11.57	9.858%	$12.7106	$12.71	$12.70	$12.70
7 purchase totals =	$985.47		$1,069.9394	$1,069.94	$1,069.90	$1,069.90