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	$19.37	11.348%	$21.5681	$21.57	$21.55	$21.60
Purchase #2	$131.46	4.140%	$136.9024	$136.90	$136.90	$136.90
Purchase #3	$97.91	13.510%	$111.1376	$111.14	$111.15	$111.10
Purchase #4	$228.51	10.390%	$252.2522	$252.25	$252.25	$252.30
Purchase #5	$43.74	6.459%	$46.5652	$46.57	$46.55	$46.60
Purchase #6	$233.99	8.267%	$253.334	$253.33	$253.35	$253.30
Purchase #7	$188.58	5.274%	$198.5257	$198.53	$198.55	$198.50
7 purchase totals =	$943.56		$1,020.2852	$1,020.29	$1,020.30	$1,020.30