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	$178.55	6.486%	$190.1308	$190.13	$190.15	$190.10
Purchase #2	$83.84	7.418%	$90.0593	$90.06	$90.05	$90.10
Purchase #3	$78.46	6.270%	$83.3794	$83.38	$83.40	$83.40
Purchase #4	$76.71	7.172%	$82.2116	$82.21	$82.20	$82.20
Purchase #5	$246.71	9.161%	$269.3111	$269.31	$269.30	$269.30
Purchase #6	$187.78	9.329%	$205.298	$205.30	$205.30	$205.30
Purchase #7	$118.80	7.727%	$127.9797	$127.98	$128.00	$128.00
7 purchase totals =	$970.85		$1,048.3699	$1,048.37	$1,048.40	$1,048.40