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	$104.51	4.611%	$109.329	$109.33	$109.35	$109.30
Purchase #2	$199.44	10.348%	$220.0781	$220.08	$220.10	$220.10
Purchase #3	$121.44	12.822%	$137.011	$137.01	$137.00	$137.00
Purchase #4	$122.81	3.819%	$127.5001	$127.50	$127.50	$127.50
Purchase #5	$212.58	7.172%	$227.8262	$227.83	$227.85	$227.80
Purchase #6	$43.67	11.804%	$48.8248	$48.82	$48.80	$48.80
Purchase #7	$79.39	13.823%	$90.3641	$90.36	$90.35	$90.40
7 purchase totals =	$883.84		$960.9333	$960.93	$960.95	$960.90