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	$123.96	12.266%	$139.1649	$139.16	$139.15	$139.20
Purchase #2	$114.58	8.710%	$124.5599	$124.56	$124.55	$124.60
Purchase #3	$218.38	3.574%	$226.1849	$226.18	$226.20	$226.20
Purchase #4	$231.86	8.210%	$250.8957	$250.90	$250.90	$250.90
Purchase #5	$38.60	4.305%	$40.2617	$40.26	$40.25	$40.30
Purchase #6	$117.77	5.121%	$123.801	$123.80	$123.80	$123.80
Purchase #7	$157.29	12.425%	$176.8333	$176.83	$176.85	$176.80
7 purchase totals =	$1,002.44		$1,081.7014	$1,081.69	$1,081.70	$1,081.80