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	$33.46	9.576%	$36.6641	$36.66	$36.65	$36.70
Purchase #2	$223.93	12.294%	$251.46	$251.46	$251.45	$251.50
Purchase #3	$111.60	8.521%	$121.1094	$121.11	$121.10	$121.10
Purchase #4	$40.90	6.623%	$43.6088	$43.61	$43.60	$43.60
Purchase #5	$160.79	3.145%	$165.8468	$165.85	$165.85	$165.80
Purchase #6	$110.57	5.746%	$116.9234	$116.92	$116.90	$116.90
Purchase #7	$72.47	8.526%	$78.6488	$78.65	$78.65	$78.60
7 purchase totals =	$753.72		$814.2613	$814.26	$814.20	$814.20