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	$141.86	10.285%	$156.4503	$156.45	$156.45	$156.50
Purchase #2	$160.49	5.809%	$169.8129	$169.81	$169.80	$169.80
Purchase #3	$73.44	12.353%	$82.512	$82.51	$82.50	$82.50
Purchase #4	$29.46	9.478%	$32.2522	$32.25	$32.25	$32.30
Purchase #5	$214.65	4.232%	$223.734	$223.73	$223.75	$223.70
Purchase #6	$87.48	8.304%	$94.7443	$94.74	$94.75	$94.70
Purchase #7	$166.33	8.184%	$179.9424	$179.94	$179.95	$179.90
7 purchase totals =	$873.71		$939.4481	$939.43	$939.45	$939.40