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	$98.80	4.658%	$103.4021	$103.40	$103.40	$103.40
Purchase #2	$148.51	10.853%	$164.6278	$164.63	$164.65	$164.60
Purchase #3	$84.38	9.319%	$92.2434	$92.24	$92.25	$92.20
Purchase #4	$192.77	9.143%	$210.395	$210.40	$210.40	$210.40
Purchase #5	$54.31	4.743%	$56.8859	$56.89	$56.90	$56.90
Purchase #6	$76.53	8.298%	$82.8805	$82.88	$82.90	$82.90
Purchase #7	$52.72	4.127%	$54.8958	$54.90	$54.90	$54.90
7 purchase totals =	$708.02		$765.3305	$765.34	$765.40	$765.30