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	$21.92	13.499%	$24.879	$24.88	$24.90	$24.90
Purchase #2	$164.88	11.341%	$183.579	$183.58	$183.60	$183.60
Purchase #3	$63.81	10.708%	$70.6428	$70.64	$70.65	$70.60
Purchase #4	$243.40	12.289%	$273.3114	$273.31	$273.30	$273.30
Purchase #5	$148.35	13.616%	$168.5493	$168.55	$168.55	$168.50
Purchase #6	$197.59	10.318%	$217.9773	$217.98	$218.00	$218.00
Purchase #7	$137.36	7.621%	$147.8282	$147.83	$147.85	$147.80
7 purchase totals =	$977.31		$1,086.7670	$1,086.77	$1,086.85	$1,086.70