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	$137.73	4.378%	$143.7598	$143.76	$143.75	$143.80
Purchase #2	$146.81	13.681%	$166.8951	$166.90	$166.90	$166.90
Purchase #3	$11.56	4.537%	$12.0845	$12.08	$12.10	$12.10
Purchase #4	$54.59	12.375%	$61.3455	$61.35	$61.35	$61.30
Purchase #5	$174.81	12.270%	$196.2592	$196.26	$196.25	$196.30
Purchase #6	$185.93	13.220%	$210.5099	$210.51	$210.50	$210.50
Purchase #7	$174.52	13.871%	$198.7277	$198.73	$198.75	$198.70
7 purchase totals =	$885.95		$989.5817	$989.59	$989.60	$989.60