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	$53.64	11.715%	$59.9239	$59.92	$59.90	$59.90
Purchase #2	$50.26	5.372%	$52.96	$52.96	$52.95	$53.00
Purchase #3	$42.32	6.202%	$44.9447	$44.94	$44.95	$44.90
Purchase #4	$177.28	8.122%	$191.6787	$191.68	$191.70	$191.70
Purchase #5	$119.45	10.661%	$132.1846	$132.18	$132.20	$132.20
Purchase #6	$41.34	10.393%	$45.6365	$45.64	$45.65	$45.60
Purchase #7	$81.47	11.164%	$90.5653	$90.57	$90.55	$90.60
7 purchase totals =	$565.76		$617.8937	$617.89	$617.90	$617.90