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	$187.74	6.842%	$200.5852	$200.59	$200.60	$200.60
Purchase #2	$121.40	9.173%	$132.536	$132.54	$132.55	$132.50
Purchase #3	$43.36	5.837%	$45.8909	$45.89	$45.90	$45.90
Purchase #4	$184.33	6.538%	$196.3815	$196.38	$196.40	$196.40
Purchase #5	$68.33	11.549%	$76.2214	$76.22	$76.20	$76.20
Purchase #6	$48.38	12.476%	$54.4159	$54.42	$54.40	$54.40
Purchase #7	$199.52	7.184%	$213.8535	$213.85	$213.85	$213.90
7 purchase totals =	$853.06		$919.8844	$919.89	$919.90	$919.90