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	$28.65	8.873%	$31.1921	$31.19	$31.20	$31.20
Purchase #2	$69.59	4.305%	$72.5858	$72.59	$72.60	$72.60
Purchase #3	$135.32	8.149%	$146.3472	$146.35	$146.35	$146.30
Purchase #4	$230.52	4.321%	$240.4808	$240.48	$240.50	$240.50
Purchase #5	$96.99	13.287%	$109.8771	$109.88	$109.90	$109.90
Purchase #6	$5.69	6.474%	$6.0584	$6.06	$6.05	$6.10
Purchase #7	$151.91	5.330%	$160.0068	$160.01	$160.00	$160.00
7 purchase totals =	$718.67		$766.5482	$766.56	$766.60	$766.60