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	$241.33	9.228%	$263.5999	$263.60	$263.60	$263.60
Purchase #2	$139.36	8.206%	$150.7959	$150.80	$150.80	$150.80
Purchase #3	$198.54	5.300%	$209.0626	$209.06	$209.05	$209.10
Purchase #4	$86.55	4.154%	$90.1453	$90.15	$90.15	$90.10
Purchase #5	$5.45	11.161%	$6.0583	$6.06	$6.05	$6.10
Purchase #6	$157.58	8.183%	$170.4748	$170.47	$170.45	$170.50
Purchase #7	$20.25	5.117%	$21.2862	$21.29	$21.30	$21.30
7 purchase totals =	$849.06		$911.4230	$911.43	$911.40	$911.50