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	$170.38	6.385%	$181.2588	$181.26	$181.25	$181.30
Purchase #2	$126.59	11.874%	$141.6213	$141.62	$141.60	$141.60
Purchase #3	$36.42	9.553%	$39.8992	$39.90	$39.90	$39.90
Purchase #4	$78.98	4.141%	$82.2506	$82.25	$82.25	$82.30
Purchase #5	$73.94	3.604%	$76.6048	$76.60	$76.60	$76.60
Purchase #6	$144.87	4.728%	$151.7195	$151.72	$151.70	$151.70
Purchase #7	$132.56	7.188%	$142.0884	$142.09	$142.10	$142.10
7 purchase totals =	$763.74		$815.4426	$815.44	$815.40	$815.50