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	$112.66	11.829%	$125.9866	$125.99	$126.00	$126.00
Purchase #2	$98.79	4.789%	$103.5211	$103.52	$103.50	$103.50
Purchase #3	$72.64	10.252%	$80.0871	$80.09	$80.10	$80.10
Purchase #4	$250.76	7.605%	$269.8303	$269.83	$269.85	$269.80
Purchase #5	$17.54	11.313%	$19.5243	$19.52	$19.50	$19.50
Purchase #6	$28.50	11.282%	$31.7154	$31.72	$31.70	$31.70
Purchase #7	$200.98	12.409%	$225.9196	$225.92	$225.90	$225.90
7 purchase totals =	$781.87		$856.5844	$856.59	$856.55	$856.50