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	$36.53	13.739%	$41.5489	$41.55	$41.55	$41.50
Purchase #2	$27.35	13.761%	$31.1136	$31.11	$31.10	$31.10
Purchase #3	$25.90	8.670%	$28.1455	$28.15	$28.15	$28.10
Purchase #4	$221.55	12.695%	$249.6758	$249.68	$249.70	$249.70
Purchase #5	$26.47	11.473%	$29.5069	$29.51	$29.50	$29.50
Purchase #6	$131.81	12.342%	$148.078	$148.08	$148.10	$148.10
Purchase #7	$38.57	6.103%	$40.9239	$40.92	$40.90	$40.90
7 purchase totals =	$508.18		$568.9926	$569.00	$569.00	$568.90