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	$51.54	5.426%	$54.3366	$54.34	$54.35	$54.30
Purchase #2	$194.79	5.245%	$205.0067	$205.01	$205.00	$205.00
Purchase #3	$34.48	12.839%	$38.9069	$38.91	$38.90	$38.90
Purchase #4	$41.73	4.321%	$43.5332	$43.53	$43.55	$43.50
Purchase #5	$41.34	3.503%	$42.7881	$42.79	$42.80	$42.80
Purchase #6	$242.50	6.547%	$258.3765	$258.38	$258.40	$258.40
Purchase #7	$125.98	9.150%	$137.5072	$137.51	$137.50	$137.50
7 purchase totals =	$732.36		$780.4552	$780.47	$780.50	$780.40