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	$96.34	12.255%	$108.1465	$108.15	$108.15	$108.10
Purchase #2	$128.84	8.382%	$139.6394	$139.64	$139.65	$139.60
Purchase #3	$89.71	7.678%	$96.5979	$96.60	$96.60	$96.60
Purchase #4	$140.81	3.642%	$145.9383	$145.94	$145.95	$145.90
Purchase #5	$24.72	13.361%	$28.0228	$28.02	$28.00	$28.00
Purchase #6	$170.78	11.617%	$190.6195	$190.62	$190.60	$190.60
Purchase #7	$131.88	8.670%	$143.314	$143.31	$143.30	$143.30
7 purchase totals =	$783.08		$852.2784	$852.28	$852.25	$852.10