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	$22.60	7.516%	$24.2986	$24.30	$24.30	$24.30
Purchase #2	$126.33	8.321%	$136.8419	$136.84	$136.85	$136.80
Purchase #3	$148.40	11.561%	$165.5565	$165.56	$165.55	$165.60
Purchase #4	$111.55	9.278%	$121.8996	$121.90	$121.90	$121.90
Purchase #5	$186.43	6.509%	$198.5647	$198.56	$198.55	$198.60
Purchase #6	$177.97	4.359%	$185.7277	$185.73	$185.75	$185.70
Purchase #7	$38.57	10.397%	$42.5801	$42.58	$42.60	$42.60
7 purchase totals =	$811.85		$875.4691	$875.47	$875.50	$875.50