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	$77.37	9.632%	$84.8223	$84.82	$84.80	$84.80
Purchase #2	$213.33	4.508%	$222.9469	$222.95	$222.95	$222.90
Purchase #3	$39.38	11.263%	$43.8154	$43.82	$43.80	$43.80
Purchase #4	$214.64	5.555%	$226.5633	$226.56	$226.55	$226.60
Purchase #5	$92.66	13.354%	$105.0338	$105.03	$105.05	$105.00
Purchase #6	$156.34	3.823%	$162.3169	$162.32	$162.30	$162.30
Purchase #7	$73.60	4.447%	$76.873	$76.87	$76.85	$76.90
7 purchase totals =	$867.32		$922.3716	$922.37	$922.30	$922.30