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	$136.37	7.509%	$146.61	$146.61	$146.60	$146.60
Purchase #2	$129.78	3.709%	$134.5935	$134.59	$134.60	$134.60
Purchase #3	$140.28	4.792%	$147.0022	$147.00	$147.00	$147.00
Purchase #4	$93.44	7.793%	$100.7218	$100.72	$100.70	$100.70
Purchase #5	$73.72	11.255%	$82.0172	$82.02	$82.00	$82.00
Purchase #6	$169.35	12.689%	$190.8388	$190.84	$190.85	$190.80
Purchase #7	$100.37	12.283%	$112.6984	$112.70	$112.70	$112.70
7 purchase totals =	$843.31		$914.4819	$914.48	$914.45	$914.40