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	$34.98	11.667%	$39.0611	$39.06	$39.05	$39.10
Purchase #2	$120.72	6.558%	$128.6368	$128.64	$128.65	$128.60
Purchase #3	$57.64	7.324%	$61.8616	$61.86	$61.85	$61.90
Purchase #4	$190.97	4.677%	$199.9017	$199.90	$199.90	$199.90
Purchase #5	$179.92	11.653%	$200.8861	$200.89	$200.90	$200.90
Purchase #6	$208.35	12.207%	$233.7833	$233.78	$233.80	$233.80
Purchase #7	$242.56	9.764%	$266.2436	$266.24	$266.25	$266.20
7 purchase totals =	$1,035.14		$1,130.3742	$1,130.37	$1,130.40	$1,130.40