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	$211.80	11.383%	$235.9092	$235.91	$235.90	$235.90
Purchase #2	$132.31	8.743%	$143.8779	$143.88	$143.90	$143.90
Purchase #3	$151.30	5.178%	$159.1343	$159.13	$159.15	$159.10
Purchase #4	$36.94	12.466%	$41.5449	$41.54	$41.55	$41.50
Purchase #5	$151.57	13.570%	$172.138	$172.14	$172.15	$172.10
Purchase #6	$18.53	12.865%	$20.9139	$20.91	$20.90	$20.90
Purchase #7	$138.89	12.312%	$155.9901	$155.99	$156.00	$156.00
7 purchase totals =	$841.34		$929.5083	$929.50	$929.55	$929.40