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	$249.43	9.390%	$272.8515	$272.85	$272.85	$272.90
Purchase #2	$53.43	4.675%	$55.9279	$55.93	$55.95	$55.90
Purchase #3	$100.89	12.484%	$113.4851	$113.49	$113.50	$113.50
Purchase #4	$43.75	4.375%	$45.6641	$45.66	$45.65	$45.70
Purchase #5	$233.46	3.728%	$242.1634	$242.16	$242.15	$242.20
Purchase #6	$121.30	10.844%	$134.4538	$134.45	$134.45	$134.50
Purchase #7	$93.42	7.611%	$100.5302	$100.53	$100.55	$100.50
7 purchase totals =	$895.68		$965.0760	$965.07	$965.10	$965.20