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	$239.64	7.872%	$258.5045	$258.50	$258.50	$258.50
Purchase #2	$54.47	6.251%	$57.8749	$57.87	$57.85	$57.90
Purchase #3	$207.58	10.576%	$229.5337	$229.53	$229.55	$229.50
Purchase #4	$5.97	9.603%	$6.5433	$6.54	$6.55	$6.50
Purchase #5	$230.34	4.301%	$240.2469	$240.25	$240.25	$240.20
Purchase #6	$87.54	5.720%	$92.5473	$92.55	$92.55	$92.50
Purchase #7	$115.39	10.225%	$127.1886	$127.19	$127.20	$127.20
7 purchase totals =	$940.93		$1,012.4392	$1,012.43	$1,012.45	$1,012.30