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	$55.37	3.456%	$57.2836	$57.28	$57.30	$57.30
Purchase #2	$107.43	3.839%	$111.5542	$111.55	$111.55	$111.60
Purchase #3	$104.81	4.681%	$109.7162	$109.72	$109.70	$109.70
Purchase #4	$171.34	13.415%	$194.3253	$194.33	$194.35	$194.30
Purchase #5	$80.29	12.558%	$90.3728	$90.37	$90.35	$90.40
Purchase #6	$145.42	12.583%	$163.7182	$163.72	$163.70	$163.70
Purchase #7	$137.67	10.142%	$151.6325	$151.63	$151.65	$151.60
7 purchase totals =	$802.33		$878.6028	$878.60	$878.60	$878.60