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	$104.69	6.867%	$111.8791	$111.88	$111.90	$111.90
Purchase #2	$180.32	11.706%	$201.4283	$201.43	$201.45	$201.40
Purchase #3	$142.91	13.262%	$161.8627	$161.86	$161.85	$161.90
Purchase #4	$141.99	5.815%	$150.2467	$150.25	$150.25	$150.20
Purchase #5	$166.58	12.128%	$186.7828	$186.78	$186.80	$186.80
Purchase #6	$181.70	13.314%	$205.8915	$205.89	$205.90	$205.90
Purchase #7	$216.76	11.256%	$241.1585	$241.16	$241.15	$241.20
7 purchase totals =	$1,134.95		$1,259.2496	$1,259.25	$1,259.30	$1,259.30