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	$164.80	11.569%	$183.8657	$183.87	$183.85	$183.90
Purchase #2	$51.89	11.396%	$57.8034	$57.80	$57.80	$57.80
Purchase #3	$138.53	6.426%	$147.4319	$147.43	$147.45	$147.40
Purchase #4	$218.35	10.389%	$241.0344	$241.03	$241.05	$241.00
Purchase #5	$189.51	3.513%	$196.1675	$196.17	$196.15	$196.20
Purchase #6	$229.34	5.420%	$241.7702	$241.77	$241.75	$241.80
Purchase #7	$16.36	12.286%	$18.37	$18.37	$18.35	$18.40
7 purchase totals =	$1,008.78		$1,086.4431	$1,086.44	$1,086.40	$1,086.50