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	$231.30	3.469%	$239.3238	$239.32	$239.30	$239.30
Purchase #2	$235.86	10.481%	$260.5805	$260.58	$260.60	$260.60
Purchase #3	$94.60	5.851%	$100.135	$100.14	$100.15	$100.10
Purchase #4	$229.38	13.293%	$259.8715	$259.87	$259.85	$259.90
Purchase #5	$16.90	8.398%	$18.3193	$18.32	$18.30	$18.30
Purchase #6	$79.37	10.362%	$87.5943	$87.59	$87.60	$87.60
Purchase #7	$156.99	5.363%	$165.4094	$165.41	$165.40	$165.40
7 purchase totals =	$1,044.40		$1,131.2338	$1,131.23	$1,131.20	$1,131.20