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	$171.79	5.397%	$181.0615	$181.06	$181.05	$181.10
Purchase #2	$233.97	9.126%	$255.3221	$255.32	$255.30	$255.30
Purchase #3	$174.89	5.397%	$184.3288	$184.33	$184.35	$184.30
Purchase #4	$150.59	3.287%	$155.5399	$155.54	$155.55	$155.50
Purchase #5	$220.73	5.696%	$233.3028	$233.30	$233.30	$233.30
Purchase #6	$164.46	11.381%	$183.1772	$183.18	$183.20	$183.20
Purchase #7	$44.28	5.617%	$46.7672	$46.77	$46.75	$46.80
7 purchase totals =	$1,160.71		$1,239.4995	$1,239.50	$1,239.50	$1,239.50