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	$51.42	8.763%	$55.9259	$55.93	$55.95	$55.90
Purchase #2	$96.39	10.231%	$106.2517	$106.25	$106.25	$106.30
Purchase #3	$150.89	7.668%	$162.4602	$162.46	$162.45	$162.50
Purchase #4	$13.47	7.857%	$14.5283	$14.53	$14.55	$14.50
Purchase #5	$26.41	8.272%	$28.5946	$28.59	$28.60	$28.60
Purchase #6	$38.46	5.389%	$40.5326	$40.53	$40.55	$40.50
Purchase #7	$97.67	3.731%	$101.3141	$101.31	$101.30	$101.30
7 purchase totals =	$474.71		$509.6074	$509.60	$509.65	$509.60