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	$12.78	8.543%	$13.8718	$13.87	$13.85	$13.90
Purchase #2	$195.66	13.390%	$221.8589	$221.86	$221.85	$221.90
Purchase #3	$79.70	12.392%	$89.5764	$89.58	$89.60	$89.60
Purchase #4	$55.63	13.546%	$63.1656	$63.17	$63.15	$63.20
Purchase #5	$141.66	7.601%	$152.4276	$152.43	$152.45	$152.40
Purchase #6	$133.32	3.426%	$137.8875	$137.89	$137.90	$137.90
Purchase #7	$159.71	13.566%	$181.3763	$181.38	$181.40	$181.40
7 purchase totals =	$778.46		$860.1641	$860.18	$860.20	$860.30