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	$93.69	12.411%	$105.3179	$105.32	$105.30	$105.30
Purchase #2	$69.73	10.210%	$76.8494	$76.85	$76.85	$76.80
Purchase #3	$26.28	5.756%	$27.7927	$27.79	$27.80	$27.80
Purchase #4	$98.76	10.270%	$108.9027	$108.90	$108.90	$108.90
Purchase #5	$230.67	10.761%	$255.4924	$255.49	$255.50	$255.50
Purchase #6	$47.43	9.380%	$51.8789	$51.88	$51.90	$51.90
Purchase #7	$248.93	12.392%	$279.7774	$279.78	$279.80	$279.80
7 purchase totals =	$815.49		$906.0114	$906.01	$906.05	$906.00