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	$133.82	4.348%	$139.6385	$139.64	$139.65	$139.60
Purchase #2	$23.48	4.565%	$24.5519	$24.55	$24.55	$24.60
Purchase #3	$85.88	9.440%	$93.9871	$93.99	$94.00	$94.00
Purchase #4	$122.95	6.666%	$131.1458	$131.15	$131.15	$131.10
Purchase #5	$163.69	7.194%	$175.4659	$175.47	$175.45	$175.50
Purchase #6	$105.40	5.436%	$111.1295	$111.13	$111.15	$111.10
Purchase #7	$175.79	7.817%	$189.5315	$189.53	$189.55	$189.50
7 purchase totals =	$811.01		$865.4502	$865.46	$865.50	$865.40