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	$12.26	13.171%	$13.8748	$13.87	$13.85	$13.90
Purchase #2	$63.81	5.746%	$67.4765	$67.48	$67.50	$67.50
Purchase #3	$52.96	9.649%	$58.0701	$58.07	$58.05	$58.10
Purchase #4	$101.92	9.766%	$111.8735	$111.87	$111.85	$111.90
Purchase #5	$193.35	11.474%	$215.535	$215.54	$215.55	$215.50
Purchase #6	$42.55	9.231%	$46.4778	$46.48	$46.50	$46.50
Purchase #7	$114.31	6.712%	$121.9825	$121.98	$122.00	$122.00
7 purchase totals =	$581.16		$635.2902	$635.29	$635.30	$635.40