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	$166.81	7.296%	$178.9805	$178.98	$179.00	$179.00
Purchase #2	$183.88	13.802%	$209.2591	$209.26	$209.25	$209.30
Purchase #3	$74.83	3.663%	$77.571	$77.57	$77.55	$77.60
Purchase #4	$116.39	5.754%	$123.0871	$123.09	$123.10	$123.10
Purchase #5	$153.35	7.270%	$164.4985	$164.50	$164.50	$164.50
Purchase #6	$101.38	7.574%	$109.0585	$109.06	$109.05	$109.10
Purchase #7	$63.74	7.632%	$68.6046	$68.60	$68.60	$68.60
7 purchase totals =	$860.38		$931.0593	$931.06	$931.05	$931.20