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	$33.66	13.290%	$38.1334	$38.13	$38.15	$38.10
Purchase #2	$80.81	5.545%	$85.2909	$85.29	$85.30	$85.30
Purchase #3	$177.51	5.399%	$187.0938	$187.09	$187.10	$187.10
Purchase #4	$31.80	10.473%	$35.1304	$35.13	$35.15	$35.10
Purchase #5	$132.89	6.517%	$141.5504	$141.55	$141.55	$141.60
Purchase #6	$240.65	11.739%	$268.8999	$268.90	$268.90	$268.90
Purchase #7	$107.36	3.523%	$111.1423	$111.14	$111.15	$111.10
7 purchase totals =	$804.68		$867.2411	$867.23	$867.30	$867.20