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	$144.41	7.588%	$155.3678	$155.37	$155.35	$155.40
Purchase #2	$43.82	9.293%	$47.8922	$47.89	$47.90	$47.90
Purchase #3	$85.70	5.464%	$90.3826	$90.38	$90.40	$90.40
Purchase #4	$133.99	3.813%	$139.099	$139.10	$139.10	$139.10
Purchase #5	$157.69	5.622%	$166.5553	$166.56	$166.55	$166.60
Purchase #6	$61.78	13.845%	$70.3334	$70.33	$70.35	$70.30
Purchase #7	$106.52	13.432%	$120.8278	$120.83	$120.85	$120.80
7 purchase totals =	$733.91		$790.4581	$790.46	$790.50	$790.50