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	$162.29	6.181%	$172.3211	$172.32	$172.30	$172.30
Purchase #2	$123.90	11.710%	$138.4087	$138.41	$138.40	$138.40
Purchase #3	$56.64	10.331%	$62.4915	$62.49	$62.50	$62.50
Purchase #4	$248.36	7.422%	$266.7933	$266.79	$266.80	$266.80
Purchase #5	$16.67	13.372%	$18.8991	$18.90	$18.90	$18.90
Purchase #6	$176.77	11.202%	$196.5718	$196.57	$196.55	$196.60
Purchase #7	$175.43	4.464%	$183.2612	$183.26	$183.25	$183.30
7 purchase totals =	$960.06		$1,038.7467	$1,038.74	$1,038.70	$1,038.80