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	$28.81	11.301%	$32.0658	$32.07	$32.05	$32.10
Purchase #2	$138.87	13.160%	$157.1453	$157.15	$157.15	$157.10
Purchase #3	$215.69	13.725%	$245.2935	$245.29	$245.30	$245.30
Purchase #4	$189.95	3.421%	$196.4482	$196.45	$196.45	$196.40
Purchase #5	$248.87	12.340%	$279.5806	$279.58	$279.60	$279.60
Purchase #6	$246.81	12.708%	$278.1746	$278.17	$278.15	$278.20
Purchase #7	$96.47	8.133%	$104.3159	$104.32	$104.30	$104.30
7 purchase totals =	$1,165.47		$1,293.0239	$1,293.03	$1,293.00	$1,293.00