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	$12.93	3.168%	$13.3396	$13.34	$13.35	$13.30
Purchase #2	$174.88	6.496%	$186.2402	$186.24	$186.25	$186.20
Purchase #3	$83.90	8.782%	$91.2681	$91.27	$91.25	$91.30
Purchase #4	$173.28	10.345%	$191.2058	$191.21	$191.20	$191.20
Purchase #5	$103.68	7.630%	$111.5908	$111.59	$111.60	$111.60
Purchase #6	$154.63	11.534%	$172.465	$172.47	$172.45	$172.50
Purchase #7	$101.42	13.455%	$115.0661	$115.07	$115.05	$115.10
7 purchase totals =	$804.72		$881.1756	$881.19	$881.15	$881.20