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	$154.35	10.364%	$170.3468	$170.35	$170.35	$170.30
Purchase #2	$85.33	4.806%	$89.431	$89.43	$89.45	$89.40
Purchase #3	$205.37	12.587%	$231.2199	$231.22	$231.20	$231.20
Purchase #4	$172.72	4.209%	$179.9898	$179.99	$180.00	$180.00
Purchase #5	$99.61	12.506%	$112.0672	$112.07	$112.05	$112.10
Purchase #6	$79.60	10.683%	$88.1037	$88.10	$88.10	$88.10
Purchase #7	$10.91	4.604%	$11.4123	$11.41	$11.40	$11.40
7 purchase totals =	$807.89		$882.5707	$882.57	$882.55	$882.50