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	$159.62	4.509%	$166.8173	$166.82	$166.80	$166.80
Purchase #2	$40.70	10.230%	$44.8636	$44.86	$44.85	$44.90
Purchase #3	$133.91	5.150%	$140.8064	$140.81	$140.80	$140.80
Purchase #4	$187.88	12.742%	$211.8197	$211.82	$211.80	$211.80
Purchase #5	$43.26	5.626%	$45.6938	$45.69	$45.70	$45.70
Purchase #6	$147.55	11.732%	$164.8606	$164.86	$164.85	$164.90
Purchase #7	$27.72	6.402%	$29.4946	$29.49	$29.50	$29.50
7 purchase totals =	$740.64		$804.3560	$804.35	$804.30	$804.40