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	$117.40	5.710%	$124.1035	$124.10	$124.10	$124.10
Purchase #2	$79.50	3.482%	$82.2682	$82.27	$82.25	$82.30
Purchase #3	$206.85	13.800%	$235.3953	$235.40	$235.40	$235.40
Purchase #4	$17.40	11.299%	$19.366	$19.37	$19.35	$19.40
Purchase #5	$21.83	12.332%	$24.5221	$24.52	$24.50	$24.50
Purchase #6	$196.54	12.683%	$221.4672	$221.47	$221.45	$221.50
Purchase #7	$219.75	7.112%	$235.3786	$235.38	$235.40	$235.40
7 purchase totals =	$859.27		$942.5009	$942.51	$942.45	$942.60