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	$134.33	6.788%	$143.4483	$143.45	$143.45	$143.40
Purchase #2	$249.83	12.347%	$280.6765	$280.68	$280.70	$280.70
Purchase #3	$236.95	5.143%	$249.1363	$249.14	$249.15	$249.10
Purchase #4	$172.83	5.217%	$181.8465	$181.85	$181.85	$181.80
Purchase #5	$131.67	9.736%	$144.4894	$144.49	$144.50	$144.50
Purchase #6	$243.61	6.584%	$259.6493	$259.65	$259.65	$259.60
Purchase #7	$222.36	4.851%	$233.1467	$233.15	$233.15	$233.10
7 purchase totals =	$1,391.58		$1,492.3930	$1,492.41	$1,492.45	$1,492.20