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	$246.44	6.144%	$261.5813	$261.58	$261.60	$261.60
Purchase #2	$132.56	3.272%	$136.8974	$136.90	$136.90	$136.90
Purchase #3	$123.79	5.744%	$130.9005	$130.90	$130.90	$130.90
Purchase #4	$93.29	11.752%	$104.2534	$104.25	$104.25	$104.30
Purchase #5	$65.92	9.278%	$72.0361	$72.04	$72.05	$72.00
Purchase #6	$22.78	5.401%	$24.0103	$24.01	$24.00	$24.00
Purchase #7	$64.58	11.253%	$71.8472	$71.85	$71.85	$71.80
7 purchase totals =	$749.36		$801.5262	$801.53	$801.55	$801.50