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	$24.41	13.129%	$27.6148	$27.61	$27.60	$27.60
Purchase #2	$166.34	10.339%	$183.5379	$183.54	$183.55	$183.50
Purchase #3	$182.98	4.275%	$190.8024	$190.80	$190.80	$190.80
Purchase #4	$214.48	6.742%	$228.9402	$228.94	$228.95	$228.90
Purchase #5	$178.87	4.812%	$187.4772	$187.48	$187.50	$187.50
Purchase #6	$96.32	9.378%	$105.3529	$105.35	$105.35	$105.40
Purchase #7	$100.47	6.321%	$106.8207	$106.82	$106.80	$106.80
7 purchase totals =	$963.87		$1,030.5461	$1,030.54	$1,030.55	$1,030.50