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	$18.64	9.774%	$20.4619	$20.46	$20.45	$20.50
Purchase #2	$169.32	7.693%	$182.3458	$182.35	$182.35	$182.30
Purchase #3	$138.79	3.486%	$143.6282	$143.63	$143.65	$143.60
Purchase #4	$89.77	12.398%	$100.8997	$100.90	$100.90	$100.90
Purchase #5	$156.35	8.267%	$169.2755	$169.28	$169.30	$169.30
Purchase #6	$132.69	9.485%	$145.2756	$145.28	$145.30	$145.30
Purchase #7	$120.33	11.344%	$133.9802	$133.98	$134.00	$134.00
7 purchase totals =	$825.89		$895.8669	$895.88	$895.95	$895.90