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	$54.59	5.192%	$57.4243	$57.42	$57.40	$57.40
Purchase #2	$210.91	3.231%	$217.7245	$217.72	$217.70	$217.70
Purchase #3	$189.86	11.585%	$211.8553	$211.86	$211.85	$211.90
Purchase #4	$79.90	9.791%	$87.723	$87.72	$87.70	$87.70
Purchase #5	$93.40	7.772%	$100.659	$100.66	$100.65	$100.70
Purchase #6	$33.70	12.622%	$37.9536	$37.95	$37.95	$38.00
Purchase #7	$57.59	12.669%	$64.8861	$64.89	$64.90	$64.90
7 purchase totals =	$719.95		$778.2258	$778.22	$778.15	$778.30