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	$30.39	11.592%	$33.9128	$33.91	$33.90	$33.90
Purchase #2	$167.80	11.787%	$187.5786	$187.58	$187.60	$187.60
Purchase #3	$160.76	7.518%	$172.8459	$172.85	$172.85	$172.80
Purchase #4	$124.36	10.855%	$137.8593	$137.86	$137.85	$137.90
Purchase #5	$95.76	7.359%	$102.807	$102.81	$102.80	$102.80
Purchase #6	$210.53	8.388%	$228.1893	$228.19	$228.20	$228.20
Purchase #7	$65.25	7.470%	$70.1242	$70.12	$70.10	$70.10
7 purchase totals =	$854.85		$933.3171	$933.32	$933.30	$933.30